In a decision that limited the use of modern privacy-threatening technology, the Supreme Court held that police much have a search warrant in order to use a thermal imager to detect patterns of heat coming from a private home.

In 1992, federal agents aimed a sensitive heat detector, the Agema Thernovision 210, at Danny Kyllo’s home in Florence, Oregon. The agents were acting on the basis of tips and utility bills suggesting the possibility that Kyllo might be growing marijuana indoors under high-intensity lamps. After the instrument registered suspicious-looking hot spots, the agents obtained a warrant to enter and search the home, where they discovered more than one hundred marijuana plants growing under lamps. Although Kyllo agreed to plead guilty of a misdemeanor requiring one month in jail, he contested the validity of the search.

The Supreme Court, by a 5-4 margin, agreed with Kyllo’s contention that the warrantless use of the thermal imager had violated his “reasonable expectation of privacy.” Writing the opinion for the Court, Justice Antonin ScaliaScalia, Antonin;Kyllo v. United States argued that the most fundamental purpose of the Fourth Amendment was to keep private homes “safe from prying government eyes,” and he emphasized the importance of not “leaving the homeowner at the mercy of advancing technology.” In a surprising dissent, Justice John Paul StevensStevens, John Paul;Kyllo v. United States, who was often called the Court’s most liberal justice, wrote that the use of the devise outside the home “did not invade any constitutionally protected interest in privacy.”

The Kyllo ruling highlighted the unpredictable nature of the Court’s line drawing when applying Fourth Amendment principles. The previous year, in Bond v. United States[c]Bond v. United States, a 7-2 majority of Court had found that the police had engaged in an unconstitutional search when they walked down the aisle of a bus and squeezed a passenger’s luggage to look for contraband. In that case, Stevens had voted with the majority, while Scalia had dissented.

Fourth Amendment

Privacy, right to

Scalia, Antonin

Search warrant requirement

Stevens, John Paul