This is an audio case brief of Kyllo v. United States, 533 U.S. 27 (2001). The audio brief provides a full case analysis. However a written summary of the case is provided below.

Table of Contents


In 1991 Agent William Elliott of the United States Department of the Interior came to suspect that marijuana was being grown in Kyllo’s home. Kyllo’s home was part of a triplex in Florence, Oregon. Indoor marijuana growth typically requires high-intensity lamps. In order to determine whether an amount of heat was emanating from Kyllo’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 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 warmth. Black is cool. White is hot. And shades of gray connote relative differences.; In that respect, the imager 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, which was across the street from the front of the house. The scan was also performed from the street in back of the house. The scan showed that the roof over the garage and a side wall of Kyllo’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 Kyllo was using halide lights to grow marijuana in his house. And 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 Kyllo’s home. During the search, the agents found an indoor growing operation involving more than 100 plants. Kyllo 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. So he entered a conditional guilty plea.


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.


Obtaining by sense-enhancing technology any information regarding the interior of the home that could not otherwise have been obtained without physical intrusion into a constitutionally protected area,, constitutes a search—at least where the technology in question is not in general public use.


The court begun its analysis by discussing how it had interpreted the fourth amendment in prior cases. The court has previously held that Fourth Amendment search does not occur—even when the explicitly protected location of a house is concerned—unless the individual manifested a subjective expectation of privacy in the object of the challenged search, and society is willing to recognize that expectation as reasonable.

But the court acknowledged that the present case involves officers on a public street engaged in more than naked-eye surveillance of a home. And It would be foolish to contend that the degree of privacy secured to citizens by the Fourth Amendment has been entirely unaffected by the advance of technology. The question the court was  confronted with then was what limits there are upon this power of technology to shrink the realm of guaranteed privacy.

The Katz test—whether the individual has an expectation of privacy that society is prepared to recognize as reasonable—has often been criticized as circular, and hence subjective and unpredictable. While it may be difficult to refine Katz when the search of areas such as telephone booths, automobiles, or even the curtilage and uncovered portions of residences is at issue, in the case of the search of the interior of homes, 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. We think that obtaining by sense-enhancing technology any information regarding the interior of the home 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. On the basis of this criterion, the information obtained by the thermal imager in this case was the product of a search.

The government however argued that the thermal imaging must be upheld because it detected only heat radiating from the external surface of the house.

But the court disagreed.

The court stated that just as a thermal imager captures only heat emanating from a house, so also a powerful directional microphone picks up only sound emanating from a house-and a satellite capable of scanning from many miles away would pick up only visible light emanating from a house. We rejected such a mechanical interpretation of the Fourth Amendment in Katz, where the eavesdropping device picked up only sound waves that reached the exterior of the phone booth. 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. While the technology used in the present case was relatively crude, the rule we adopt must take account of more sophisticated systems that are already in use or in development.

Next the government argued that the thermal imaging was constitutional because it did not detect private activities occurring in private areas. The government  pointed out that in Dow Chemicals v. United Sates, the court that the enhanced aerial photography did not reveal any “intimate details.”

But the court again disagreed with the government’s contention.

The court explained that in Dow Chemical involved enhanced aerial photography of an industrial complex, which does not share the Fourth Amendment sanctity of the home. The Fourth Amendment’s protection of the home has never been tied to measurement of the quality or quantity of information obtained. In the home, our cases show, all details are intimate details, because the entire area is held safe from prying government eyes.

Limiting the prohibition of thermal imaging to “intimate details” would not only be wrong in principle; it would be impractical in application, failing to provide “a workable accommodation between the needs of law enforcement and the interests protected by the Fourth Amendment.

To begin with, there is no necessary connection between the sophistication of the surveillance equipment and the “intimacy” of the details that it observes—which means that one cannot say (and the police cannot be assured) that use of the relatively crude equipment at issue here will always be lawful.


The court held that the officers conduct was a search that required a warrant.

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