Full text copy of the 1/23/2012 Supreme Court decision in what has been described as "the most important Fourth Amendment case in a decade."
SCOTUS unanimously decided (in United States v. Jones, three separate opinions) that the warrantless tracking of a suspect's vehicle by GPS was in fact unconstitutional.
Interesting: "In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory, but practical. Traditional surveillance for any extended period of time was difficult and costly and therefore rarely undertaken. The surveillance at issue in this case—constant monitoring of the location of a vehicle for four weeks—would have required a large team of agents, multiple vehicles, and perhaps aerial assistance. Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources. Devices like the one used in the present case, however, make long-term monitoring relatively easy and cheap. In circumstances involving dramatic technological change, the best solution to privacy concerns may be legislative. See, e.g., Kerr, 102 Mich. L. Rev., at 805–806. A legislative body is well situated to gauge changing public attitudes, to draw detailed lines, and to balance privacy and public safety in a comprehensive way..."