More interesting than the decision—in which Scalia so narrows the scope of the case (to whether attaching a device to a car constitutes a search) that it's pretty boring—are last November's oral arguments.[1a, 1b]
In the oral arguments, there's considerable discussion about whether pervasive GPS or other technologically enabled surveillance in itself is constitutionally permitted. The discussion on this point makes for interesting listening/reading because everyone agrees that the police are permitted persistently to monitor someone over any indefinitely long period (in public, where there is no search) without a warrant. Would equivalent surveillance carried out not by human police officers but rather by technology be allowed? Even though the relevant technologies will soon be so cheap that the authorities would be able to monitor anyone (or everyone) in the country?
Another interesting point brought up in the oral arguments is that the government owns your license plate, so placing a monitoring device on that, rather than the car itself, would not constitute a trespass and so may not constitute a search. Nothing in this decision refutes that logic, so the police may still be able to track you by GPS without a warrant so long as they put the transmitter on your license plate.
In the oral arguments, there's considerable discussion about whether pervasive GPS or other technologically enabled surveillance in itself is constitutionally permitted. The discussion on this point makes for interesting listening/reading because everyone agrees that the police are permitted persistently to monitor someone over any indefinitely long period (in public, where there is no search) without a warrant. Would equivalent surveillance carried out not by human police officers but rather by technology be allowed? Even though the relevant technologies will soon be so cheap that the authorities would be able to monitor anyone (or everyone) in the country?
Another interesting point brought up in the oral arguments is that the government owns your license plate, so placing a monitoring device on that, rather than the car itself, would not constitute a trespass and so may not constitute a search. Nothing in this decision refutes that logic, so the police may still be able to track you by GPS without a warrant so long as they put the transmitter on your license plate.
1a. Transcript: Oral Argument - Supreme Court [PDF]
1b. Audio: http://www.c-spanvideo.org/program/302576-1 [Flash]