Orin Kerr provides his analysis and views on the issue over on The Volokh Conspiracy.
Does the Fourth Amendment require a warrant to conduct surveillance of a government-installed GPS device, such as a device installed on a suspect’s car to monitor the car’s location? This issue comes up occasionally, and the DC Circuit has a case pending on the issue. I don’t think I have ever blogged about it, so I want to offer my thoughts. This post will explain why I think the doctrine here was settled by a pair of Supreme court cases from the 1980s, and why those cases draw a pretty reasonable Fourth Amendment line.
In the 1980s, the Supreme Court decided two cases on whether the Fourth Amendment requires a warrant for the government to monitor a suspect’s location using a government-installed locating device. Both cases involved beepers, defined as “a radio transmitter, usually battery-operated, which emits periodic signals that can be picked up by a radio receiver.” The combined holding of United States v. Knotts, 460 U.S. 276 (1983), and United States v. Karo, 468 U.S. 705 (1984), was that the constitutionality of warrantless beeper surveillance depends on what information the beeper reveals. Beeper surveillance that reveals the location of the beeper in a public place does not require a warrant (Knotts); on the other hand, beeper surveillance that reveals the location of the beeper inside a home does require a warrant (Karo).
Read more on The Volokh Conspiracy.
Update: See also John Wesley Hall, Jr.’s commentary on FourthAmendment.com