"In Kyllo [v United States], a federal agent used infrared thermal imaging equipment to compare the heat emanating from a triplex unit to the heat signatures of other nearby residences. Based in part on the equipment reading indicating that the defendant’s home was warmer than the others, the agent obtained a search warrant. Officers searched the home and seized marijuana plants growing inside. The government argued that the Fourth Amendment had no application, because the defendant had made no effort to conceal the heat escaping the walls of his home and had no reasonable expectation that passers-by would not take notice.
"The Supreme Court disagreed, 5-4, holding that the use of sense-enhancing technology not in general public use, in order to reveal details about the interior of a private home that could not otherwise be ascertained without entering the home, constitutes a search. The majority placed great emphasis on the fact that the technique was aimed at a private dwelling, yet it is not clear from the decision whether (or why) the use of such technology against a barn or private office should yield a different result."
Best, Richard A., Jr.; Elsea, Jennifer K., "Satellite Surveillance: Domestic Issues," Congressional Research Service (Washington, DC: Library of Congress, January 13, 2011), p. 15.