533 U.S. 27 (2001)
In 1991 Agent William Elliott of the United States Department of the Interior came to suspect that marijuana was being grown in the home belonging to petitioner Danny Kyllo, part of a triplex on Rhododendron Drive in Florence, Oregon.1 Indoor marijuana growth typically requires high-intensity lamps.2
At 3:20 a.m. on January 16, 1992, Agent Elliott and Dan Haas used an Agema Thermovision 210 thermal imager to scan the triplex.3 The scan was performed from the passenger seat of Agent Elliott’s vehicle across the street from the front of the house and also from the street in back of the house.4 Thermal imagers detect infrared radiation, which virtually all objects emit but which is not visible to the naked eye.5 The imager converts radiation into images based on relative warmth—black is cool, white is hot, shades of gray connote relative differences.6
The scan of Kyllo’s home took only a few minutes. It showed that the roof over the garage and a side wall of petitioner’s home were relatively hot compared to the rest of the home and substantially warmer than neighboring homes in the triplex.7 Based on tips from informants, utility bills, and the thermal imaging, a Federal Magistrate Judge issued a warrant authorizing a search of petitioner’s home.8 The agents found an indoor growing operation involving more than 100 plants.9
Petitioner was indicted on one count of manufacturing marijuana in violation of 21 U.S.C. § 841(a)(1).10 He unsuccessfully moved to suppress the evidence seized from his home and then entered a conditional guilty plea.11 The Court of Appeals for the Ninth Circuit remanded the case for an evidentiary hearing regarding the intrusiveness of thermal imaging.12 On remand the District Court found that the Agema 210 is a non-intrusive device which emits no rays or beams and shows a crude visual image of the heat being radiated from the outside of the house.13 It did not show any people or activity within the walls of the structure.14 No intimate details of the home were observed.15 A divided Court of Appeals initially reversed, but that opinion was withdrawn and the panel affirmed.16 The Supreme Court granted certiorari.17
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?18
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.19
Yes. The rule applies directly because Agent Elliott employed the Agema Thermovision 210 thermal imager, a device not in general public use, from a public street to measure relative heat levels emanating from Kyllo’s home.20 That measurement revealed information about activity inside the home, specifically the use of high-intensity halide lamps for marijuana cultivation, that could not have been acquired without physical entry into the constitutionally protected area of the residence.21
The thermal imaging therefore constituted a search within the meaning of the Fourth Amendment.22
Related opinions on this issue
Justice Stevens dissented on the ground that the thermal imaging involved only off-the-wall observations of heat emissions already exposed to the public domain rather than any through-the-wall penetration of the home.23 He stressed that the device passively measured relative differences in heat radiating from exterior surfaces without invading the interior or obtaining information regarding activities inside the residence.24 In Stevens's view, drawing inferences from such publicly exposed data does not constitute a search because heat waves enter the public domain once they leave the building.25
He further argued that a strong public interest supports allowing officials to monitor emissions such as excessive heat without erecting constitutional barriers.26 Stevens criticized the majority's new rule as unnecessary, overly broad, and inconsistent with established precedent that protects against actual physical intrusions rather than external measurements.27 He concluded that the officers' conduct amounted to nothing more than reasonable off-the-wall surveillance.28