The article links to the relevant Supreme Court decision. They, in "Kyllo v. United States, 533 U.S. 27 (2001), held that the use of a thermal imaging, or FLIR,

The article links to the relevant Supreme Court decision. They, in "Kyllo v. United States, 533 U.S. 27 (2001), held that the use of a thermal imaging, or FLIR, device from a public vantage point to monitor the radiation of heat from a person's home was a "search" within the meaning of the Fourth Amendment, and thus required a warrant." -http://en.wikipedia.org/wiki/Kyllo_v._United_States http://en.wikipedia.org/wiki/Kyllo_v._United_States The article goes on to say the Supreme Court "specifically noted that the rule would apply to radar-based systems that were then being developed."