In August 2010, the U.S. Court of Appeals for the Ninth Circuit in San Francisco, California, headed by Chief Judge Alex Kozinski, who dissented, ruled that home driveways are still public to mailmen, delivery people, children and strangers and thus, the police have a right, without violating the Fourth Amendment, to secretly place GPS devices on cars in driveways and track those cars - without a warrant.
http://www.earthfiles.com/news.php?ID=1764&category=Environment