[1] 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.

[4] 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.

[11] 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.

[12] 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.

[13] 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.

[14] In a dissenting opinion authored by Justice John Paul Stevens, the minority argued that the use of thermal imaging does not constitute a Fourth Amendment "search" because any person could detect the heat emissions.

"[21] Stevens especially criticized Scalia's invocation of the bright line test, calling it "unnecessary, unwise, and inconsistent with the Fourth Amendment," because this would be defunct as soon as the surveillance technology used by the police against Kyllo went into general public use.

[18][24] Orin Kerr wrote that such phrases "can be read plausibly as suggesting a broad and even creative view of how the Fourth Amendment should respond when technology threatens privacy.

[5] During oral arguments in the Kyllo case, Justice Sandra Day O'Connor posed that dog sniffs would be considered unconstitutional if compared to thermal imaging, despite the Supreme Court previously upholding their constitutionality in United States v. Place (1983).

[36] In 2013, the Supreme Court held in Florida v. Jardines that drug-sniffing police dogs could not be brought to the front door of a person's house without a search warrant, but based this argument on the law of trespass against property rather than a right to privacy.