Kyllo v. United States
Decided June 11, 2001, 533 U.S. 27

Use of thermal-imaging devices to monitor heat emissions from a private residence in order to monitor activities occurring inside the home is a Fourth Amendment 'search,' and it is presumptively unreasonable without a warrant.


A. Issues Discussed:
Search and seizure

B. Legal Question Presented:

Does 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 constitute a "search" within the meaning of the Fourth Amendment and if so, was the search unreasonable without a warrant?


A. Background:

"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."

On certiorari, the U.S. Supreme Court reversed the judgment of the United States Court of Appeals for the Ninth Circuit.

B. Counsel of Record:
Opposing Side
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
C. The Arguments:
Opposing Side
Unavailable Unavailable
Opposing Side

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.


The Supreme Court held that:

"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...

This Court has approved warrantless visual surveillance of a home, ruling that visual observation is no 'search' at all. In assessing when a search is not a search, the Court has adapted a principle first enunciated in Katz v. United States: A 'search' does not occur--even when its object is a house explicitly protected by the Fourth Amendment--unless the individual manifested a subjective expectation of privacy in the searched object, and society is willing to recognize that expectation as reasonable...

[I]n 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,' 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.

Based on this criterion, the information obtained by the thermal imager in this case was the product of a search... 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.

... 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."

The United States Supreme Court reversed the United States Court of Appeals for the Ninth Circuit judgment.

Justice Vote: 5 Pro vs. 4 Con
  • Scalia, A. Pro (Wrote majority opinion)
  • Souter, D. Pro (Joined majority opinion)
  • Thomas, C. Pro (Joined majority opinion)
  • Ginsburg, R. Pro (Joined majority opinion)
  • Breyer, S. Pro (Joined majority opinion)
  • Stevens, J. Con (Wrote dissenting opinion)
  • Rehnquist, W. Con (Joined dissenting opinion)
  • O'Connor, S. Con (Joined dissenting opinion)
  • Kennedy, A. Con (Joined dissenting opinion)

    The ACLU, as amicus curiae, urged reversal of the judgment of the United States Court of Appeals for the Ninth Circuit; the Supreme Court reversed in a 5-4 vote, giving the ACLU an apparent win.