NACDL has an interesting News Release, Civil Liberties, Religious Groups Seek to Require Warrants for Police GPS Surveillance.
The law is constantly adjusting to technology — the phone tap, the pen register, the thermal imaging device, are one of many items to get into your house. We've commented earlier about the use of cellphone tracking technology on where and how to find you. In each of the technology questions lies the issue of choice, or lack thereof.
George Orwell, 1984, how right was he/is he?
NACDL has a good site for Warrantless Domestic Spying issues.