An advanced form of eavesdropping. Electronic surveillance employs sophisticated electronic equipment to intercept private conversations or observe conduct that is meant to be private. It includes the use of small radio transmitters or "bugs" to listen in on telephone or in-person conversations, the use of lasers to intercept conversations inside a room from the slight vibrations of the window glass, and the use of thermal imaging scopes for observing conduct inside a structure. Many of these sophisticated forms of surveillance require a search warrant because they violate a person's reasonable expectation of privacy. This area of law is in a constant state of flux as courts interpret the use of new technologies.