Kyllo v. United States, 533 U.S. 27 (2001), was a decision by the Supreme Court of the United States in which the court ruled that the use of thermal imaging devices to monitor heat radiation in or around a person's home, even if conducted from a public vantage point, is unconstitutional without a search warrant. In its majority opinion, the court held that thermal imaging constitutes a "search" under the Fourth Amendment, as the police were using devices to "explore details of the home that would previously have been unknowable without physical intrusion." The ruling has been noted for refining the reasonable expectation of privacy doctrine in light of new surveillance technologies, and when those are used in areas that are accessible to the public.
Background
In 1991, federal agents with the United States Department of the Interior received a tip that Danny Lee Kyllo was growing marijuana in his home in Florence, Oregon. The agents used an FLIR thermal imaging device outside Kyllo's home, which revealed unusual heat patterns and an unusual amount of heat radiating from the roof and side walls compared with the rest of the house, leading the agents to believe he was using high-intensity halide lamps that are common in cannabis cultivation. The scan was conducted from a parked car across the street, without a search warrant. The thermograms gathered from the scan were used to obtain a warrant for a subsequent search of the house, and during that search federal agents found more than 100 marijuana plants. Kyllo was charged with one count of manufacturing marijuana.
At a preliminary hearing, the court denied Kyllo's motion to suppress the evidence obtained from the thermal imaging search, ruling that the device could not "penetrate walls or windows to reveal conversations or human activities" and that the device "recorded only heat being emitted from the home". Kyllo entered a conditional guilty plea before appealing to the Ninth Circuit Court of Appeals on the grounds that observations with a thermal-imaging device constituted a search under the Fourth Amendment. The Ninth Circuit ultimately upheld admission of the evidence and allowed criminal trying proceedings to continue. Kyllo then petitioned the Supreme Court for a writ of certiorari, which was granted in 2000.
Opinion of the Court
At the Supreme Court, the government defended the use of thermal imaging technology on two grounds: first, that thermal imaging was not an invasion of privacy, because the devices could not reveal any intimate details of the home; and second, that heat radiation can be detected in several ways from a public vantage point without the aid of technology, such as observing snow melt or smoke rise.
In a majority opinion written by Justice Antonin Scalia, the Supreme Court ruled that the thermal imaging of Kyllo's home constituted a "search" within the meaning of the Fourth Amendment. By a 5–4 margin, the court held that a search warrant must be obtained before the government, including the police and federal agents, may use a thermal imaging device to monitor the heat and radiation of one's home. Scalia also noted the surveillance powers that could be abused by the police with technologies that are "not in general public use". As the police did not have a warrant when they used the device outside of Kyllo's home, the search was unconstitutional.
Scalia wrote: "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." The majority opinion argued that a person has an expectation of privacy in his or her home, and therefore, the government cannot conduct unreasonable searches, even with technology that does not enter the home.
The Kyllo decision, relying on Katz v. United States (1967), confirmed the expectation of privacy in one's home, and limited the means by which the government can explore the home without a warrant. Scalia referred to the firm but bright line drawn at the entrance of a home, where the Fourth Amendment is said to recognize a heightened expectation of privacy. Furthermore, Scalia discussed how future technologies could invade one's right of privacy. Scalia argued that the Framers of the Constitution would agree that such technology would be intrusive enough to warrant a search, if they knew it existed, and as such, that technology (including thermal imaging) calls for the same warrant requirements as physical intrusion.