In a 5-4 decision that crosses the traditional ideological divisions of the justices, the US Supreme Court has decided that the Fourth Amendment covers the infrared imaging of private dwellings. As a result, law enforcement professionals will need a warrant to conduct thermal surveillance on a residence.

The court found that infrared imaging constitutes a search because it enables the user to be privy to the goings-on within a space that is socially and reasonably expected to be private. The decision is proactive, citing the more sophisticated surveillance techniques in development. "The question we confront today is what limits there are upon this power of technology to shrink the realm of guaranteed privacy," wrote Justice Antonin Scalia in the majority opinion.

The case stems from the 1992 arrest of Danny Kyllo of Florence, Ore., for "manufacturing marijuana" in his home. Federal agents obtained a search warrant to enter the residence based in part on information they had collected with a thermal imager that suggested the presence of high-intensity halide grow lamps.