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

Federal agents suspected defendant Kyllo of growing marijuana in his home, part of a triplex. Indoor marijuana production requires high-intensity heat lamps. In order to determine if such lamps were in use at Kyllo’s home, agents used a thermal imager to determine the relative amount of heat emanating from Kyllo’s triplex. The scan was done from the agent’s car across the street and took only a couple of minutes. The scan revealed that the roof and one wall of Kyllo’s garage were relatively hot compared with the rest of the home and the rest of the triplex. Based on tips from informants, utility bills, and the thermal scan, a search warrant was issued. More than 100 marijuana plants were discovered in Kyllo’s home. He moved unsuccessfully to have the evidence from the thermal scan suppressed and was convicted, and he appealed. The Court of Appeals for the Ninth Circuit remanded the case to the district court to decide on the intrusiveness of the thermal scanning. The district court held that it was not intrusive because, inter alia, it did not reveal intimate details of the home. The district court upheld the warrant, and the defendant again appealed. The Ninth Circuit eventually affirmed the decision under the Katz v. United States test, holding that Kyllo had shown no subjective expectation of privacy in the amount of heat escaping from his home, and even if he had, there was no reasonable expectation of privacy in “amorphous ‘hot spots’ on the roof and exterior wall.”
The United States Supreme Court granted certiorari and reversed the Court of Appeals for the Ninth Circuit. The Court held that where the government uses a device that is not in general public use to explore the details of a private home that would have been unknowable but for physical intrusion, the surveillance constitutes a “search” within the meaning of the Fourth Amendment. In an opinion delivered by Justice Scalia, the Court arrived at this conclusion by applying the Katz “reasonable expectation” test: an object is not protected from search by the Fourth Amendment unless the individual has a subjective expectation of privacy in the searched object, and society is willing to recognize that expectation as reasonable. The Fourth Amendment is most applicable to the protection of privacy interests in the home, but is extended to protect against searches of many things in which an individual has an expectation of privacy. Indeed, in Katz the Court found an impermissible search in the government’s use of a “listening device” planted in a public phone booth. While the setting is not a home, and is not always particularly private because passersby may hear what is transpiring, an individual who shuts the door to a public phone booth has a subjective expectation of privacy in the conversation, and society is prepared to recognize that as reasonable.
While visual observation is not a search, this case involved more than naked-eye surveillance; it involved the use of technology. And whereas the Court had previously held that enhanced aerial photography of an industrial complex was not a search—primarily because it was not a home, where privacy expectations are heightened (Dow Chemical Co. v. United States)—here the Court drew the line. It held that any information obtained by sense-enhancing technology regarding the interior of the home, that could not have otherwise been obtained without physical intrusion, constitutes a search. The Court declined to adopt the argument that the type of information, intimate versus non-intimate, required a different conclusion. The Court ruled that all details of the home are intimate details. The Court affirmed that the Fourth Amendment draws a firm line at the entrance to the house, and that line must be not only firm but bright, requiring clear specification of what methods of surveillance are impermissibly intrusive without a warrant.
Justice Stevens, joined by Chief Justice Rehnquist and Justices Kennedy and O’Connor, dissented. The dissent in this case argued that there was an overlooked distinction between “through-the-wall surveillance” and “off-the-wall surveillance.” It argued that the thermal scanning, which collected data exposed on the outside of the home, did not invade any constitutionally protected interest in privacy. Moreover, the dissent argued that the majority’s holding was contrary to established law: that what a person knowingly exposes to the public is not subject to Fourth Amendment protection. The dissent compared heat waves to aromas from a kitchen, a lab, or an opium den: they enter the public domain when they leave a building, and the expectation that they would remain private is not one that society would recognize as reasonable. The dissent likened this case to California v. Greenwood (1979), in which the court held that there is no reasonable expectation of privacy warranting Fourth Amendment protection in garbage discarded on the curb outside the home. Further, the dissent argued that the majority’s limitation of Fourth Amendment protection to surveillance by technology not in the public use makes the holding meaningless because the protection dissipates as soon as the technology becomes publicly available. The dissent also faulted the majority for making their holding “home-specific,” citing the proposition that the Fourth Amendment protects people, not places. The dissent concluded with an argument that while the Court was properly concerned about threats to privacy flowing from advances in technology, the duty to grapple with these issues belongs to the legislature.