New technologies of surveillance such as Global Positioning Systems (GPS) are increasingly used as convenient substitutes for conventional means of observation. Recent court decisions hold that the government may, without a warrant, use a GPS to track a vehicle’s movements in public places without violating the 4th Amendment, as the vehicle is in plain view and no reasonable expectation of privacy is violated. This emerging consensus of opinions fails to distinguish the unreasonable expectation that we not be seen in public, (...) from the reasonable expectation that we not be followed. Drawing on a critical discussion of the plain view doctrine, analysis of privacy interests in public places, and distinguishing privacy from property interests, the article contends that government use of GPS to track our movements should require a warrant. (shrink)