OCTOBER TERM, 2000
Syllabus
KYLLO
v. UNITED STATES
CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE NINTH
CIRCUIT
No. 99-8508. Argued February 20, 200l-Decided June 11,2001
Suspicious that marijuana was being grown in petitioner Kyllo's
home in a triplex, agents used a thermal-imaging device to scan the
triplex to determine if the amount of heat emanating from it was
consistent with the high-intensity lamps typically used for indoor
marijuana growth. The scan showed that Kyllo's garage roof and a
side wall were relatively hot compared to the rest of his home and
substantially warmer than the neighboring units. Based in part on
the thermal imaging, a Federal Magistrate Judge issued a warrant to
search Kyllo's home, where the agents found marijuana growing.
After Kyllo was indicted on a federal drug charge, he
unsuccessfully moved to suppress the evidence seized from his home
and then entered a conditional guilty plea. The Ninth Circuit
ultimately affirmed, upholding the thermal imaging on the ground
that Kyllo had shown no subjective expectation of privacy because
he had made no attempt to conceal the heat escaping from his home.
Even if he had, ruled the court, there was no objectively
reasonable expectation of privacy because the thermal imager did
not expose any intimate details of Kyllo's life, only amorphous hot
spots on his home's exterior.
Held: Where, as here, the Government uses a device that
is not in general public use, to explore details of a private home
that would previously have been unknowable without physical
intrusion, the surveillance is a Fourth Amendment "search," and is
presumptively unreasonable without a warrant. Pp. 31-41.
(a) The question whether a warrantless search of a home is
reasonable and hence constitutional must be answered no in most
instances, but the antecedent question whether a Fourth Amendment
"search" has occurred is not so simple. This Court has approved
warrantless visual surveillance of a home, see
California v.
Ciraolo, 476
U. S. 207, 213, ruling that visual observation is no "search"
at all, see
Dow Chemical Co. v.
United States,
476 U. S. 227,
234-235, 239. In assessing when a search is not a search, the Court
has adapted a principle first enunciated in
Katz v.
United States, 389 U. S. 347, 361: A
"search" does not occur-even when its object is a house explicitly
protected by the Fourth Amendment-unless the individual manifested
a subjective
28
Syllabus
expectation of privacy in the searched object, and society is
willing to recognize that expectation as reasonable, see,
e. g.,
California v.
Ciraolo, supra, at 211. Pp. 31-33.
(b) While it may be difficult to refine the
Katz test in
some instances, in the case of the search of a home's interior-the
prototypical and hence most commonly litigated area of protected
privacy-there is a ready criterion, with roots deep in the common
law, of the minimal expectation of privacy that
exists, and
that is acknowledged to be
reasonable. To withdraw
protection of this minimum expectation would be to permit police
technology to erode the privacy guaranteed by the Fourth Amendment.
Thus, obtaining by sense-enhancing technology any information
regarding the home's interior that could not otherwise have been
obtained without physical "intrusion into a constitutionally
protected area,"
Silverman v.
United States, 365 U. S. 505, 512,
constitutes a search-at least where (as here) the technology in
question is not in general public use. This assures preservation of
that degree of privacy against government that existed when the
Fourth Amendment was adopted. Pp. 33-35.
(c) Based on this criterion, the information obtained by the
thermal imager in this case was the product of a search. The Court
rejects the Government's argument that the thermal imaging must be
upheld because it detected only heat radiating from the home's
external surface. Such a mechanical interpretation of the Fourth
Amendment was rejected in
Katz, where the eavesdropping
device in question picked up only sound waves that reached the
exterior of the phone booth to which it was attached. Reversing
that approach would leave the homeowner at the mercy of advancing
technology-including imaging technology that could discern all
human activity in the home. Also rejected is the Government's
contention that the thermal imaging was constitutional because it
did not detect "intimate details." Such an approach would be wrong
in principle because, in the sanctity of the home,
all
details are intimate details. See,
e. g., United States v.
Karo, 468 U. S.
705; Dow Chemical, supra, at 238,
distinguished. It would also be impractical in application, failing
to provide a workable accommodation between law enforcement needs
and Fourth Amendment interests. See
Oliver v.
United
States, 466 U. S.
170, 181. Pp. 35-40.
(d) Since the imaging in this case was an unlawful search, it
will remain for the District Court to determine whether, without
the evidence it provided, the search warrant was supported by
probable cause-and if not, whether there is any other basis for
supporting admission of that evidence. P. 40.
190 F.3d
1041, reversed and remanded.
29
SCALIA, J., delivered the opinion of the Court, in which SOUTER,
THOMAS, GINSBURG, and BREYER, JJ., joined. STEVENS, J., filed a
dissenting opinion, in which REHNQUIST, C. J., and O'CONNOR and
KENNEDY, JJ., joined,
post, p. 41.
Kenneth Lerner, by appointment of the Court, 531 U. S.
955, argued the cause and filed briefs for petitioner.
Deputy Solicitor General Dreeben argued the cause for the United
States. With him on the brief were former Solicitor General Waxman,
Assistant Attorney General Robinson, Irving L. Gornstein, and
Deborah Watson. *
JUSTICE SCALIA delivered the opinion of the Court.
This case presents the question whether the use of a
thermal-imaging device aimed at a private home from a public street
to detect relative amounts of heat within the home constitutes a
"search" within the meaning of the Fourth Amendment.
I
In 1991 Agent William Elliott of the United States Department of
the Interior came to suspect that marijuana was being grown in the
home belonging to petitioner Danny Kyllo, part of a triplex on
Rhododendron Drive in Florence, Oregon. Indoor marijuana growth
typically requires highintensity lamps. In order to determine
whether an amount of heat was emanating from petitioner's home
consistent with the use of such lamps, at 3:20 a.m. on January 16,
1992, Agent Elliott and Dan Haas used an Agema Thermovision 210
thermal imager to scan the triplex. Thermal imagers detect infrared
radiation, which virtually all objects emit but which is not
visible to the naked eye. The imager converts radiation into images
based on relative warmth-black
*Briefs of
amici curiae urging reversal were filed for
the Liberty Project by
Julie M. Carpenter; and for the
National Association of Criminal Defense Lawyers et al. by
James J.
Tomkovicz, Lisa B. Kemler, and
Steven R.
Shapiro.
30
is cool, white is hot, shades of gray connote relative
differences; in that respect, it operates somewhat like a video
camera showing heat images. The scan of Kyllo's home took only a
few minutes and was performed from the passenger seat of Agent
Elliott's vehicle across the street from the front of the house and
also from the street in back of the house. The scan showed that the
roof over the garage and a side wall of petitioner's home were
relatively hot compared to the rest of the home and substantially
warmer than neighboring homes in the triplex. Agent Elliott
concluded that petitioner was using halide lights to grow marijuana
in his house, which indeed he was. Based on tips from informants,
utility bills, and the thermal imaging, a Federal Magistrate Judge
issued a warrant authorizing a search of petitioner's home, and the
agents found an indoor growing operation involving more than 100
plants. Petitioner was indicted on one count of manufacturing
marijuana, in violation of 21 U. s. C. § 841(a)(1). He
unsuccessfully moved to suppress the evidence seized from his home
and then entered a conditional guilty plea.
The Court of Appeals for the Ninth Circuit remanded the case for
an evidentiary hearing regarding the intrusiveness of thermal
imaging. On remand the District Court found that the Agema 210 "is
a non-intrusive device which emits no rays or beams and shows a
crude visual image of the heat being radiated from the outside of
the house"; it "did not show any people or activity within the
walls of the structure"; "[t]he device used cannot penetrate walls
or windows to reveal conversations or human activities"; and "[n]o
intimate details of the home were observed." Supp. App. to Pet. for
Cert. 39-40. Based on these findings, the District Court upheld the
validity of the warrant that relied in part upon the thermal
imaging, and reaffirmed its denial of the motion to suppress. A
divided Court of Appeals initially reversed,
140
F.3d 1249 (1998), but that
31
opinion was withdrawn and the panel (after a change in
composition) affirmed,
190 F.3d
1041 (1999), with Judge Noonan dissenting. The court held that
petitioner had shown no subjective expectation of privacy because
he had made no attempt to conceal the heat escaping from his home,
id., at 1046, and even if he had, there was no objectively
reasonable expectation of privacy because the imager "did not
expose any intimate details of Kyllo's life," only "amorphous 'hot
spots' on the roof and exterior wall," id., at 1047. We granted
certiorari. 530 U. S. 1305 (2000).
II
The Fourth Amendment provides that "[t]he right of the people to
be secure in their persons, houses, papers, and effects, against
unreasonable searches and seizures, shall not be violated." "At the
very core" of the Fourth Amendment "stands the right of a man to
retreat into his own home and there be free from unreasonable
governmental intrusion."
Silverman v.
United States,
365 U. S. 505,
511 (1961). With few exceptions, the question whether a warrantless
search of a home is reasonable and hence constitutional must be
answered no. See
Illinois v.
Rodriguez, 497 U. S. 177, 181
(1990);
Payton v.
New York, 445 U. S. 573, 586
(1980).
On the other hand, the antecedent question whether or not a
Fourth Amendment "search" has occurred is not so simple under our
precedent. The permissibility of ordinary visual surveillance of a
home used to be clear because, well into the 20th century, our
Fourth Amendment jurisprudence was tied to common-law trespass.
See,
e. g., Goldman v.
United States, 316 U. S. 129, 134-136
(1942);
Olmstead v.
United States, 277 U. S. 438, 464-466
(1928). Cf.
Silverman v.
United States, supra, at
510-512 (technical trespass not necessary for Fourth Amendment
violation; it suffices if there is "actual intrusion into a
constitutionally protected area"). Visual surveillance was
unquestionably lawful because" 'the
32
eye cannot by the laws of England be guilty of a trespass.'"
Boyd v.
United States, 116 U. S. 616, 628 (1886)
(quoting
Entick v.
Carrington, 19 How. St. Tr. 1029,
95 Eng. Rep. 807 (K. B. 1765)). We have since decoupled violation
of a person's Fourth Amendment rights from trespassory violation of
his property, see
Rakas v.
III inois, 439 U. S. 128, 143
(1978), but the lawfulness of warrantless visual surveillance of a
home has still been preserved. As we observed in
California
v.
Ciraolo, 476 U. S. 207, 213
(1986), "[t]he Fourth Amendment protection of the home has never
been extended to require law enforcement officers to shield their
eyes when passing by a home on public thoroughfares."
One might think that the new validating rationale would be that
examining the portion of a house that is in plain public view,
while it is a "search" 1 despite the absence of trespass, is not an
"unreasonable" one under the Fourth Amendment. See
Minnesota
v.
Carter, 525
U. S. 83, 104 (1998) (BREYER, J., concurring in judgment). But
in fact we have held that visual observation is no "search" at
allperhaps in order to preserve somewhat more intact our doctrine
that warrantless searches are presumptively unconstitutional. See
Dow Chemical Co. v.
United States, 476 U. S. 227,
234-235, 239 (1986). In assessing when a search is not a search, we
have applied somewhat in reverse the principle first enunciated in
Katz v.
United States, 389 U. S. 347 (1967).
Katz involved eavesdropping by means of an electronic
listening device placed on the outside of a telephone booth-a
location not within the catalog ("persons, houses, papers, and
effects") that the Fourth Amendment protects against unreasonable
searches. We held that the
1 When the Fourth Amendment was adopted, as now, to "search"
meant "[tJo look over or through for the purpose of finding
something; to explore; to examine by inspection; as, to
search the house for a book; to
search the wood for a
thief." N. Webster, An American Dictionary of the English Language
66 (1828) (reprint 6th ed. 1989).
33
Fourth Amendment nonetheless protected Katz from the warrantless
eavesdropping because he "justifiably relied" upon the privacy of
the telephone booth.
Id., at 353. As Justice Harlan's
oft-quoted concurrence described it, a Fourth Amendment search
occurs when the government violates a subjective expectation of
privacy that society recognizes as reasonable. See id., at 361. We
have subsequently applied this principle to hold that a Fourth
Amendment search does
not occur-even when the explicitly
protected location of a
house is concerned-unless "the
individual manifested a subjective expectation of privacy in the
object of the challenged search," and "society [is] willing to
recognize that expectation as reasonable."
Ciraolo, supra,
at 211. We have applied this test in holding that it is not a
search for the police to use a pen register at the phone company to
determine what numbers were dialed in a private home,
Smith
v.
Maryland, 442 U. S. 735, 743744
(1979), and we have applied the test on two different occasions in
holding that aerial surveillance of private homes and surrounding
areas does not constitute a search,
Ciraolo, supra; Florida
v.
Riley, 488
U. S. 445 (1989).
The present case involves officers on a public street engaged in
more than naked-eye surveillance of a home. We have previously
reserved judgment as to how much technological enhancement of
ordinary perception from such a vantage point, if any, is too much.
While we upheld enhanced aerial photography of an industrial
complex in
Dow Chemical, we noted that we found "it
important that this is
not an area immediately adjacent to a
private home, where privacy expectations are most heightened," 476
U. S., at 237, n. 4 (emphasis in original).
III
It would be foolish to contend that the degree of privacy
secured to citizens by the Fourth Amendment has been
34
entirely unaffected by the advance of technology. For example,
as the cases discussed above make clear, the technology enabling
human flight has exposed to public view (and hence, we have said,
to official observation) uncovered portions of the house and its
curtilage that once were private. See
Ciraolo, supra, at
215. The question we confront today is what limits there are upon
this power of technology to shrink the realm of guaranteed
privacy.
The
Katz test-whether the individual has an expectation
of privacy that society is prepared to recognize as reasonable-has
often been criticized as circular, and hence subjective and
unpredictable. See 1 W. LaFave, Search and Seizure § 2.1(d), pp.
393-394 (3d ed. 1996); Posner, The Uncertain Protection of Privacy
by the Supreme Court, 1979 S. Ct. Rev. 173, 188;
Carter,
supra, at 97 (SCALIA, J., concurring). But see
Rakas,
supra, at 143-144, n.12. While it may be difficult to refine
Katz when the search of areas such as telephone booths,
automobiles, or even the curtilage and uncovered portions of
residences is at issue, in the case of the search of the interior
of homes-the prototypical and hence most commonly litigated area of
protected privacythere is a ready criterion, with roots deep in the
common law, of the minimal expectation of privacy that
exists, and that is acknowledged to be
reasonable. To
withdraw protection of this minimum expectation would be to permit
police technology to erode the privacy guaranteed by the Fourth
Amendment. We think that obtaining by senseenhancing technology any
information regarding the interior of the home that could not
otherwise have been obtained without physical "intrusion into a
constitutionally protected area,"
Silverman, 365 U. S., at
512, constitutes a searchat least where (as here) the technology in
question is not in general public use. This assures preservation of
that degree of privacy against government that existed when the
Fourth Amendment was adopted. On the basis of this criterion,
the
35
information obtained by the thermal imager in this case was the
product of a search.2
The Government maintains, however, that the thermal imaging must
be upheld because it detected "only heat radiating from the
external surface of the house," Brief for United States 26. The
dissent makes this its leading point, see
post, at 41,
contending that there is a fundamental difference between what it
calls "off-the-wall" observations and "through-the-wall
surveillance." But just as a thermal imager captures only heat
emanating from a house, so also a powerful directional microphone
picks up only sound emanating from a house-and a satellite capable
of scanning from many miles away would pick up only visible light
emanating from a house. We rejected such a mechanical
interpretation of the Fourth Amendment in
Katz, where the
eavesdropping device picked up only sound waves that reached the
exterior of the phone booth. Reversing that approach would leave
the homeowner at the mercy of advancing technologyincluding imaging
technology that could discern all human
2 The dissent's repeated assertion that the thermal imaging did
not obtain information regarding the interior of the home,
post, at 43, 44 (opinion of STEVENS, J.), is simply
inaccurate. A thermal imager reveals the relative heat of various
rooms in the home. The dissent may not find that information
particularly private or important, see
post, at 43-44, 45,
4950, but there is no basis for saying it is not information
regarding the interior of the home. The dissent's comparison of the
thermal imaging to various circumstances in which outside observers
might be able to perceive, without technology, the heat of the
home-for example, by observing snowmelt on the roof,
post,
at 43-is quite irrelevant. The fact that equivalent information
could sometimes be obtained by other means does not make lawful the
use of means that violate the Fourth Amendment. The police might,
for example, learn how many people are in a particular house by
setting up year-round surveillance; but that does not make breaking
and entering to find out the same information lawful. In any event,
on the night of January 16, 1992, no outside observer could have
discerned the relative heat of Kyllo's home without thermal
imaging.
36
activity in the home. While the technology used in the present
case was relatively crude, the rule we adopt must take account of
more sophisticated systems that are already in use or in
development.3 The dissent's reliance on the distinction between
"off-the-wall" and "through-the-wall" observation is entirely
incompatible with the dissent's belief, which we discuss below,
that thermal-imaging observations of the intimate details of a home
are impermissible. The most sophisticated thermal-imaging devices
continue to measure heat "off-the-wall" rather than
"through-the-wall"; the dissent's disapproval of those more
sophisticated thermalimaging devices, see
post, at 49, is an
acknowledgment that there is no substance to this distinction. As
for the dissent's extraordinary assertion that anything learned
through "an inference" cannot be a search, see
post, at 44,
that would validate even the "through-the-wall" technologies that
the dissent purports to disapprove. Surely the dissent does not
believe that the through-the-wall radar or ultrasound technology
produces an 8-by-10 Kodak glossy that needs no analysis (i.
e., the making of inferences). And, of course, the novel
proposition that inference insulates a search is blatantly contrary
to
United States v.
Karo, 468 U. S. 705 (1984),
where the police "inferred" from the activation of a beeper that a
certain can of ether was in the home. The police ac-
3 The ability to "see" through walls and other opaque barriers
is a clear, and scientifically feasible, goal of law enforcement
research and development. The National Law Enforcement and
Corrections Technology Center, a program within the United States
Department of Justice, features on its Internet Website projects
that include a "RadarBased Through-the-Wall Surveillance System,"
"Handheld Ultrasound Through the Wall Surveillance," and a "Radar
Flashlight" that "will enable law enforcement officers to detect
individuals through interior building walls."
www.nlectc.org/techproj/
(visited May 3, 2001). Some devices may emit low levels of
radiation that travel "through-the-wall," but others, such as more
sophisticated thermal-imaging devices, are entirely passive, or
"off-the-wall" as the dissent puts it.
37
tivity was held to be a search, and the search was held
unlawfu1.4
The Government also contends that the thermal imaging was
constitutional because it did not "detect private activities
occurring in private areas," Brief for United States 22. It points
out that in
Dow Chemical we observed that the enhanced
aerial photography did not reveal any "intimate details." 476 U.
S., at 238.
Dow Chemical, however, involved enhanced aerial
photography of an industrial complex, which does not share the
Fourth Amendment sanctity of the home. The Fourth Amendment's
protection of the home has never been tied to measurement of the
quality or quantity of information obtained. In
Silverman,
for example, we made clear that any physical invasion of the
structure of the home, "by even a fraction of an inch," was too
much, 365 U. S., at 512, and there is certainly no exception to the
warrant requirement for the officer who barely cracks open the
front door and sees nothing but the nonintimate rug on the
vestibule floor. In the home, our cases show,
all details
are intimate details, because the entire area is held safe from
prying government eyes. Thus, in
Karo, supra, the only thing
detected was a can of ether in the
4 The dissent asserts,
post, at 44-45, n. 3, that we have
misunderstood its point, which is not that inference
insulates a search, but that inference alone is
not a
search. If we misunderstood the point, it was only in a good-faith
effort to render the point germane to the case at hand. The issue
in this case is not the police's allegedly unlawful inferencing,
but their allegedly unlawful thermal-imaging measurement of the
emanations from a house. We say such measurement is a search; the
dissent says it is not, because an inference is not a search. We
took that to mean that, since the technologically enhanced
emanations had to be the basis of inferences before anything inside
the house could be known, the use of the emanations could not be a
search. But the dissent certainly knows better than we what it
intends. And if it means only that an inference is not a search, we
certainly agree. That has no bearing, however, upon whether hi-tech
measurement of emanations from a house is a search.
38
home; and in
Arizona v.
Hicks, 480 U. S. 321 (1987), the
only thing detected by a physical search that went beyond what
officers lawfully present could observe in "plain view" was the
registration number of a phonograph turntable. These were intimate
details because they were details of the home, just as was the
detail of how warm-or even how relatively warm-Kyllo was heating
his residence.5
Limiting the prohibition of thermal imaging to "intimate
details" would not only be wrong in principle; it would be
impractical in application, failing to provide "a workable
accommodation between the needs of law enforcement and the
interests protected by the Fourth Amendment,"
Oliver v.
United States, 466 U. S. 170, 181
(1984). To begin with, there is no necessary connection between the
sophistication of the surveillance equipment and the "intimacy" of
the details that it observes-which means that one cannot say (and
the police cannot be assured) that use of the relatively crude
equipment at issue here will always be lawful. The Agema
Thermovision 210 might disclose, for example, at what hour each
night the lady of the house takes her daily sauna and bath-a detail
that many would consider "intimate"; and a much more sophisticated
system might detect nothing more intimate than the fact that
someone left a closet light on. We could not, in other words,
develop a rule approving only that through-the-wall surveillance
which identifies objects no smaller than 36 by 36 inches, but would
have to develop a jurisprudence specifying which
5The Government cites our statement in
California v.
Ciraolo, 476 U. S. 207 (1986), noting apparent agreement
with the State of California that aerial surveillance of a house's
curtilage could become "'invasive'" if "'modern technology'"
revealed "'those intimate associations, objects or activities
otherwise imperceptible to police or fellow citizens.'"
Id.,
at 215, n. 3 (quoting Brief for State of California 14-15). We
think the Court's focus in this secondhand dictum was not upon
intimacy but upon otherwise-imperceptibility, which is precisely
the principle we vindicate today.
39
home activities are "intimate" and which are not. And even when
(if ever) that jurisprudence were fully developed, no police
officer would be able to know
in advance whether his
through-the-wall surveillance picks up "intimate" detailsand thus
would be unable to know in advance whether it is
constitutional.
The dissent's proposed standard-whether the technology offers
the "functional equivalent of actual presence in the area being
searched,"
post, at 47-would seem quite similar to our own
at first blush. The dissent concludes that
Katz was such a
case, but then inexplicably asserts that if the same listening
device only revealed the volume of the conversation, the
surveillance would be permissible,
post, at 49-50. Yet if,
without technology, the police could not discern volume without
being actually present in the phone booth, JUSTICE STEVENS should
conclude a search has occurred. Cf.
Karo, 468 U. S., at 735
(STEVENS, J., concurring in part and dissenting in part) ("I find
little comfort in the Court's notion that no invasion of privacy
occurs until a listener obtains some significant information by use
of the device .... A bathtub is a less private area when the
plumber is present even if his back is turned"). The same should
hold for the interior heat of the home if only a person present in
the home could discern the heat. Thus the driving force of the
dissent, despite its recitation of the above standard, appears to
be a distinction among different types of information-whether the
"homeowner would even care if anybody noticed,"
post, at 50.
The dissent offers no practical guidance for the application of
this standard, and for reasons already discussed, we believe there
can be none. The people in their houses, as well as the police,
deserve more precision.6
6 The dissent argues that we have injected potential uncertainty
into the constitutional analysis by noting that whether or not the
technology is in general public use may be a factor. See
post, at 47. That quarrel,
40
We have said that the Fourth Amendment draws "a firm line at the
entrance to the house,"
Payton, 445 U. S., at 590. That
line, we think, must be not only firm but also brightwhich requires
clear specification of those methods of surveillance that require a
warrant. While it is certainly possible to conclude from the
videotape of the thermal imaging that occurred in this case that no
"significant" compromise of the homeowner's privacy has occurred,
we must take the long view, from the original meaning of the Fourth
Amendment forward.
"The Fourth Amendment is to be construed in the light of what
was deemed an unreasonable search and seizure when it was adopted,
and in a manner which will conserve public interests as well as the
interests and rights of individual citizens." Carroll v.
United States, 267 U. S. 132, 149 (1925).
Where, as here, the Government uses a device that is not in
general public use, to explore details of the home that would
previously have been unknowable without physical intrusion, the
surveillance is a "search" and is presumptively unreasonable
without a warrant.
Since we hold the Thermovision imaging to have been an unlawful
search, it will remain for the District Court to determine whether,
without the evidence it provided, the search warrant issued in this
case was supported by probable cause-and if not, whether there is
any other basis for supporting admission of the evidence that the
search pursuant to the warrant produced.
however, is not with us but with this Court's precedent. See
Ciraolo, supra, at 215 ("In an age where private and
commercial flight in the public airways is routine, it is
unreasonable for respondent to expect that his marijuana plants
were constitutionally protected from being observed with the naked
eye from an altitude of 1,000 feet"). Given that we can quite
confidently say that thermal imaging is not "routine," we decline
in this case to reexamine that factor.
41
***
The judgment of the Court of Appeals is reversed; the case is
remanded for further proceedings consistent with this opinion.
It is so ordered.
JUSTICE STEVENS, with whom THE CHIEF JUSTICE, JusTICE O'CONNOR,
and JUSTICE KENNEDY join, dissenting.
There is, in my judgment, a distinction of constitutional
magnitude between "through-the-wall surveillance" that gives the
observer or listener direct access to information in a private
area, on the one hand, and the thought processes used to draw
inferences from information in the public domain, on the other
hand. The Court has crafted a rule that purports to deal with
direct observations of the inside of the home, but the case before
us merely involves indirect deductions from "off-the-wall"
surveillance, that is, observations of the exterior of the home.
Those observations were made with a fairly primitive thermal imager
that gathered data exposed on the outside of petitioner's home but
did not invade any constitutionally protected interest in privacy.l
Moreover, I believe that the supposedly "bright-line" rule the
Court has created in response to its concerns about future
technological developments is unnecessary, unwise, and inconsistent
with the Fourth Amendment.
I
There is no need for the Court to craft a new rule to decide
this case, as it is controlled by established principles from
1 After an evidentiary hearing, the District Court found:
"[T]he use of the thermal imaging device here was not an
intrusion into Kyllo's home. No intimate details of the home were
observed, and there was no intrusion upon the privacy of the
individuals within the home. The device used cannot penetrate walls
or windows to reveal conversations or human activities. The device
recorded only the heat being emitted from the home." Supp. App. to
Pet. for Cert. 40.
42
our Fourth Amendment jurisprudence. One of those core
principles, of course, is that "searches and seizures
inside a
home without a warrant are presumptively unreasonable."
Payton v.
New York, 445 U. S. 573, 586 (1980)
(emphasis added). But it is equally well settled that searches and
seizures of property in plain view are presumptively reasonable.
See id., at 586-587.2 Whether that property is residential or
commercial, the basic principle is the same: "'What a person
knowingly exposes to the public, even in his own home or office, is
not a subject of Fourth Amendment protection.'"
California
v.
Ciraolo, 476 U. S. 207, 213 (1986)
(quoting
Katz v.
United States, 389 U. S. 347, 351
(1967)); see
Florida v.
Riley, 488 U. S. 445, 449-450
(1989); California v.
Greenwood, 486 U. S. 35, 40-41
(1988);
Dow Chemical Co. v.
United States, 476 U. S. 227, 235-236
(1986); Air Pollution Variance Bd. of Colo. v.
Western
Alfalfa Corp., 416 U. S. 861, 865
(1974). That is the principle implicated here.
While the Court "take[s] the long view" and decides this case
based largely on the potential of yet-to-be-developed technology
that might allow "through-the-wall surveillance,"
ante, at
38-40; see
ante, at 36, n. 3, this case involves nothing
more than off-the-wall surveillance by law enforcement officers to
gather information exposed to the general public from the outside
of petitioner's home. All that the infrared camera did in this case
was passively measure heat emitted
2 Thus, for example, we have found consistent with the Fourth
Amendment, even absent a warrant, the search and seizure of garbage
left for collection outside the curtilage of a home,
California v.
Greenwood, 486 U. S. 35 (1988); the
aerial surveillance of a fenced-in backyard from an altitude of
1,000 feet,
California v.
Ciraolo, 476 U. S. 207 (1986); the
aerial observation of a partially exposed interior of a residential
greenhouse from 400 feet above,
Florida v.
Riley,
488 U. S. 445
(1989); the aerial photography of an industrial complex from
several thousand feet above,
Dow Chemical Co. v.
United
States, 476 U. S.
227 (1986); and the observation of smoke emanating from chimney
stacks,
Air Pollution Variance Bd. of Colo. v.
Western
Alfalfa Corp., 416 U. S. 861 (1974).
43
from the exterior surfaces of petitioner's home; all that those
measurements showed were relative differences in emission levels,
vaguely indicating that some areas of the roof and outside walls
were warmer than others. As still images from the infrared scans
show, see Appendix,
infra, no details regarding the interior
of petitioner's home were revealed. Unlike an x-ray scan, or other
possible "throughthe-wall" techniques, the detection of infrared
radiation emanating from the home did not accomplish "an
unauthorized physical penetration into the premises,"
Silverman v.
United States, 365 U. S. 505, 509
(1961), nor did it "obtain information that it could not have
obtained by observation from outside the curtilage of the house,"
United States v.
Karo, 468 U. S. 705, 715
(1984).
Indeed, the ordinary use of the senses might enable a neighbor
or passerby to notice the heat emanating from a building,
particularly if it is vented, as was the case here. Additionally,
any member of the public might notice that one part of a house is
warmer than another part or a nearby building if, for example,
rainwater evaporates or snow melts at different rates across its
surfaces. Such use of the senses would not convert into an
unreasonable search if, instead, an adjoining neighbor allowed an
officer onto her property to verify her perceptions with a
sensitive thermometer. Nor, in my view, does such observation
become an unreasonable search if made from a distance with the aid
of a device that merely discloses that the exterior of one house,
or one area of the house, is much warmer than another. Nothing more
occurred in this case.
Thus, the notion that heat emissions from the outside of a
dwelling are a private matter implicating the protections of the
Fourth Amendment (the text of which guarantees the right of people
"to be secure
in their ... houses" against unreasonable
searches and seizures (emphasis added)) is not only unprecedented
but also quite difficult to take seriously. Heat waves, like aromas
that are generated in a kitchen, or
44
in a laboratory or opium den, enter the public domain if and
when they leave a building. A subjective expectation that they
would remain private is not only implausible but also surely not
"one that society is prepared to recognize as 'reasonable.'"
Katz, 389 U. S., at 361 (Harlan, J., concurring).
To be sure, the homeowner has a reasonable expectation of
privacy concerning what takes place within the home, and the Fourth
Amendment's protection against physical invasions of the home
should apply to their functional equivalent. But the equipment in
this case did not penetrate the walls of petitioner's home, and
while it did pick up "details of the home" that were exposed to the
public,
ante, at 38, it did not obtain "any information
regarding the
interior of the home,"
ante, at 34
(emphasis added). In the Court's own words, based on what the
thermal imager "showed" regarding the outside of petitioner's home,
the officers "concluded" that petitioner was engaging in illegal
activity inside the home.
Ante, at 30. It would be quite
absurd to characterize their thought processes as "searches,"
regardless of whether they inferred (rightly) that petitioner was
growing marijuana in his house, or (wrongly) that "the lady of the
house [was taking] her daily sauna and bath."
Ante, at 38.
In either case, the only conclusions the officers reached
concerning the interior of the home were at least as indirect as
those that might have been inferred from the contents of discarded
garbage, see
California v.
Greenwood, 486 U. S. 35 (1988), or
pen register data, see
Smith v.
Maryland, 442 U. S. 735 (1979), or,
as in this case, subpoenaed utility records, see
190 F.3d
1041, 1043 (CA9 1999). For the first time in its history, the
Court assumes that an inference can amount to a Fourth Amendment
violation. See
ante, at 36-37.3
3 Although the Court credits us with the "novel proposition that
inference insulates a search,"
ante, at 36, our point simply
is that an inference cannot
be a search, contrary to the
Court's reasoning. See
supra this page. Thus, the Court's
use of
United States v.
Karo, 468 U. S. 705
45
Notwithstanding the implications of today's decision, there is a
strong public interest in avoiding constitutional litigation over
the monitoring of emissions from homes, and over the inferences
drawn from such monitoring. Just as "the police cannot reasonably
be expected to avert their eyes from evidence of criminal activity
that could have been observed by any member of the public,"
Greenwood, 486 U. S., at 41, so too public officials should
not have to avert their senses or their equipment from detecting
emissions in the public domain such as excessive heat, traces of
smoke, suspicious odors, odorless gases, airborne particulates, or
radioactive emissions, any of which could identify hazards to the
community. In my judgment, monitoring such emissions with
"sense-enhancing technology,"
ante, at 34, and drawing
useful conclusions from such monitoring, is an entirely reasonable
public service.
On the other hand, the countervailing privacy interest is at
best trivial. After all, homes generally are insulated to keep heat
in, rather than to prevent the detection of heat going out, and it
does not seem to me that society will suffer from a rule requiring
the rare homeowner who both intends to engage in uncommon
activities that produce extraordinary amounts of heat, and wishes
to conceal that production from outsiders, to make sure that the
surrounding area is well insulated. Cf.
United States v.
Jacobsen, 466
U. S. 109, 122 (1984) ("The concept of an interest in privacy
that society is prepared to recognize as reasonable is, by its very
nature, critically different from the mere expectation, however
well
(1984), to refute a point we do not make underscores the fact
that the Court has no real answer (either in logic or in law) to
the point we do make. Of course,
Karo itself does not
provide any support for the Court's view that inferences can amount
to unconstitutional searches. The illegality in that case was "the
monitoring of a beeper in a private residence" to obtain
information that "could not have [been] obtained by observation
from outside," id., at 714-715, rather than any thought processes
that flowed from such monitoring.
46
justified, that certain facts will not come to the attention of
the authorities"). The interest in concealing the heat escaping
from one's house pales in significance to "the chief evil against
which the wording of the Fourth Amendment is directed," the
"physical entry of the home,"
United States v.
United
States Dist. Court for Eastern Dist. of Mich., 407 U. S. 297,
313 (1972), and it is hard to believe that it is an interest the
Framers sought to protect in our Constitution.
Since what was involved in this case was nothing more than
drawing inferences from off-the-wall surveillance, rather than any
"through-the-wall" surveillance, the officers' conduct did not
amount to a search and was perfectly reasonable.4
II
Instead of trying to answer the question whether the use of the
thermal imager in this case was even arguably unreasonable, the
Court has fashioned a rule that is intended to provide essential
guidance for the day when "more sophisticated systems" gain the
"ability to 'see' through walls and other opaque barriers."
Ante, at 36, and n. 3. The newly minted rule encompasses
"obtaining [1] by senseenhancing technology [2] any information
regarding the interior of the home [3] that could not otherwise
have been obtained without physical intrusion into a
constitutionally protected area ... [4] at least where (as here)
the technology in question is not in general public use."
Ante, at 34 (internal quotation marks omitted). In my
judgment, the
4 This view comports with that of all the Courts of Appeals that
have resolved the issue. See
190 F.3d
1041 (CA9 1999);
United States v.
Robinson, 62 F.3d
1325 (CAll 1995) (upholding warrantless use of thermal imager);
United States v.
Myers, 46 F.3d
668 (CA7 1995) (same);
United States v.
Ishmael, 48 F.3d
850 (CA5 1995) (same);
United States v.
Pinson, 24 F.3d
1056 (CA8 1994) (same). But see
United States v.
Cusumano, 67 F.3d
1497 (CAW 1995) (warrantless use of thermal imager violated
Fourth Amendment), vacated and decided on other grounds,
83 F.3d
1247 (CAW 1996) (en bane).
47
Court's new rule is at once too broad and too narrow, and is not
justified by the Court's explanation for its adoption. As I have
suggested, I would not erect a constitutional impediment to the use
of sense-enhancing technology unless it provides its user with the
functional equivalent of actual presence in the area being
searched.
Despite the Court's attempt to draw a line that is "not only
firm but also bright,"
ante, at 40, the contours of its new
rule are uncertain because its protection apparently dissipates as
soon as the relevant technology is "in general public use,"
ante, at 34. Yet how much use is general public use is not
even hinted at by the Court's opinion, which makes the somewhat
doubtful assumption that the thermal imager used in this case does
not satisfy that criterion.5 In any event, putting aside its lack
of clarity, this criterion is somewhat perverse because it seems
likely that the threat to privacy will grow, rather than recede, as
the use of intrusive equipment becomes more readily available.
It is clear, however, that the category of "sense-enhancing
technology" covered by the new rule,
ibid., is far too
broad. It would, for example, embrace potential mechanical
substitutes for dogs trained to react when they sniff narcotics.
But in
United States v.
Place, 462 U. S. 696, 707
(1983), we held that a dog sniff that "discloses only the presence
or absence of narcotics" does "not constitute a 'search' within the
meaning of the Fourth Amendment," and it must follow that
sense-enhancing equipment that identifies nothing but illegal
5 The record describes a device that numbers close to a thousand
manufactured units; that has a predecessor numbering in the
neighborhood of 4,000 to 5,000 units; that competes with a similar
product numbering from 5,000 to 6,000 units; and that is "readily
available to the public" for commercial, personal, or law
enforcement purposes, and is just an 800number away from being
rented from "half a dozen national companies" by anyone who wants
one. App. 18. Since, by virtue of the Court's new rule, the issue
is one of first impression, perhaps it should order an evidentiary
hearing to determine whether these facts suffice to establish
"general public use."
48
activity is not a search either. Nevertheless, the use of such a
device would be unconstitutional under the Court's rule, as would
the use of other new devices that might detect the odor of deadly
bacteria or chemicals for making a new type of high explosive, even
if the devices (like the dog sniffs) are "so limited both in the
manner in which" they obtain information and "in the content of the
information" they reveal.
Ibid. If nothing more than that
sort of information could be obtained by using the devices in a
public place to monitor emissions from a house, then their use
would be no more objectionable than the use of the thermal imager
in this case.
The application of the Court's new rule to "any information
regarding the interior of the home,"
ante, at 34, is also
unnecessarily broad. If it takes sensitive equipment to detect an
odor that identifies criminal conduct and nothing else, the fact
that the odor emanates from the interior of a home should not
provide it with constitutional protection. See
supra, at 47
and this page. The criterion, moreover, is too sweeping in that
information "regarding" the interior of a home apparently is not
just information obtained through its walls, but also information
concerning the outside of the building that could lead to (however
many) inferences "regarding" what might be inside. Under that
expansive view, I suppose, an officer using an infrared camera to
observe a man silently entering the side door of a house at night
carrying a pizza might conclude that its interior is now occupied
by someone who likes pizza, and by doing so the officer would be
guilty of conducting an unconstitutional "search" of the home.
Because the new rule applies to information regarding the
"interior" of the home, it is too narrow as well as too broad.
Clearly, a rule that is designed to protect individuals from the
overly intrusive use of sense-enhancing equipment should not be
limited to a home. If such equipment
49
did provide its user with the functional equivalent of access to
a private place-such as, for example, the telephone booth involved
in
Katz, or an office building-then the rule should apply to
such an area as well as to a home. See
Katz, 389 U. S., at
351 ("[T]he Fourth Amendment protects people, not places").
The final requirement of the Court's new rule, that the
information "could not otherwise have been obtained without
physical intrusion into a constitutionally protected area,"
ante, at 34 (internal quotation marks omitted), also extends
too far as the Court applies it. As noted, the Court effectively
treats the mental process of analyzing data obtained from external
sources as the equivalent of a physical intrusion into the home.
See
supra, at 44. As I have explained, however, the process
of drawing inferences from data in the public domain should not be
characterized as a search.
The two reasons advanced by the Court as justifications for the
adoption of its new rule are both unpersuasive. First, the Court
suggests that its rule is compelled by our holding in
Katz,
because in that case, as in this, the surveillance consisted of
nothing more than the monitoring of waves emanating from a private
area into the public domain. See
ante, at 35. Yet there are
critical differences between the cases. In
Katz, the
electronic listening device attached to the outside of the phone
booth allowed the officers to pick up the content of the
conversation inside the booth, making them the functional
equivalent of intruders because they gathered information that was
otherwise available only to someone inside the private area; it
would be as if, in this case, the thermal imager presented a view
of the heat-generating activity inside petitioner's home. By
contrast, the thermal imager here disclosed only the relative
amounts of heat radiating from the house; it would be as if, in
Katz, the listening device disclosed only the rela-
50
tive volume of sound leaving the booth, which presumably was
discernible in the public domain.6 Surely, there is a significant
difference between the general and well-settled expectation that
strangers will not have direct access to the contents of private
communications, on the one hand, and the rather theoretical
expectation that an occasional homeowner would even care if anybody
noticed the relative amounts of heat emanating from the walls of
his house, on the other. It is pure hyperbole for the Court to
suggest that refusing to extend the holding of
Katz to this
case would leave the homeowner at the mercy of "technology that
could discern all human activity in the home."
Ante, at
35-36.
Second, the Court argues that the permissibility of
"through-the-wall surveillance" cannot depend on a distinction
between observing "intimate details" such as "the lady of the house
[taking] her daily sauna and bath," and noticing only "the
nonintimate rug on the vestibule floor" or "objects no smaller than
36 by 36 inches."
Ante, at 37, 3839. This entire argument
assumes, of course, that the thermal imager in this case could or
did perform "through-thewall surveillance" that could identify any
detail "that would previously have been unknowable without physical
intrusion."
Ante, at 39-40. In fact, the device could not,
see n. 1,
supra, and did not, see Appendix,
infra,
enable its user to identify either the lady of the house, the rug
on the vestibule floor, or anything else inside the house, whether
smaller or larger than 36 by 36 inches. Indeed, the vague thermal
images of petitioner's home that are reproduced in the Appendix
were submitted by him to the District Court as part of an expert
report raising the question whether the device could even take
"accurate, consistent infrared images" of the
6 The use of the latter device would be constitutional given
Smith v.
Maryland, 442 U. S. 735, 741
(1979), which upheld the use of pen registers to record numbers
dialed on a phone because, unlike "the listening device employed in
Katz ... pen registers do not acquire the
contents of
communications."
51
outside of his house. Defendant's Exh. 107, p. 4. But
even if the device could reliably show extraordinary differences in
the amounts of heat leaving his home, drawing the inference that
there was something suspicious occurring inside the residence-a
conclusion that officers far less gifted than Sherlock Holmes would
readily draw-does not qualify as "through-the-wall surveillance,"
much less a Fourth Amendment violation.
III
Although the Court is properly and commendably concerned about
the threats to privacy that may flow from advances in the
technology available to the law enforcement profession, it has
unfortunately failed to heed the tried and true counsel of judicial
restraint. Instead of concentrating on the rather mundane issue
that is actually presented by the case before it, the Court has
endeavored to craft an all-encompassing rule for the future. It
would be far wiser to give legislators an unimpeded opportunity to
grapple with these emerging issues rather than to shackle them with
prematurely devised constitutional constraints.
I respectfully dissent.
[Appendix to opinion of STEVENS, J., follows this page.]
52
Appendix to opinion of STEVENS, J.
APPENDIX TO OPINION OF STEVENS, J. (Images and text reproduced
from defendant's exhibit 107) Top left: Infrared image of a video
frame from the videotape submitted as evidence in this case. The
thermogram indicates the suspect house as it appeared with the Gain
and contrast in its default setting. Only the outline of the house
is visible. The camera used was the Thermovision 210. Top Right:
Infrared image of a subsequent videoframe taken from the videotape.
The gain and contrast settings have been increased in order to make
the walls and roof of the structure appear hotter than what it
actually is.
Bottom Left: Infrared image of the opposite side of the suspects
house. The thermogram is also taken from the same videotape. The
camera settings are in the default mode and the outline of the
house is barely visible. Only the hot electrical transformer and
the street light are identifiable.
Bottom Right: The same image, but with the gain and contrast
increased. This change in camera settings cause any object to
appear hotter than what it actually is. The arrow indicates the
overloading of an area immediately around a hot object in this case
the electrical transformer and the streetlight. This overloading of
the image is an inherent design flaw in the camera itself.
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