Stevens, J., dissenting
SUPREME COURT OF THE UNITED STATES
 No. 99-8508
 DANNY LEE KYLLO, PETITIONER v. UNITED STATES
ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
THE NINTH CIRCUIT
[June 11, 2001]
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.1 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 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 11-12; see ante, at 8, 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 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.

SUPREME COURT OF THE UNITED STATES
 No. 99-8508
 DANNY LEE KYLLO, PETITIONER v. UNITED STATES
ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
THE NINTH CIRCUIT
[June 11, 2001]
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 high-intensity 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 warmth­black 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 opinion was
withdrawn and the panel (after a change in composition) affirmed, 190 F.3d 1041 (1999),

SUPREME COURT OF THE UNITED STATES
KYLLO v. UNITED STATES
CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE NINTH
CIRCUIT
 No. 99-8508. Argued February 20, 2001­Decided 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. 3-13.
(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 occur­even when its object is a house explicitly protected by
the Fourth Amendment­unless the individual manifested a subjective 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. 3-5.
(b) While it may be difficult to refine the Katz test in some instances, in the case of the
search of a home's interior­the 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. 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 search­at least where
(as here) the technology in question is not in general public use. This assures preservation