In its 2001 decision Kyllo v. United States, a sharply divided (5–4) Court ruled that the use of a thermal imager was a search within the meaning of the Fourth Amendment. This means that the government cannot use a thermal imager to scan a home without first obtaining a warrant. In somewhat of a surprise, Justice Antonin Scalia wrote for the majority: “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.”