Kyllo v. United States, 533 U.S. 27, 2 (2001)

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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.

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