Government Use GPS to Track Your Moves on your own car.

Government agents can sneak onto your property in the middle of the night, put a GPS device on the bottom of your car and keep track of everywhere you go. This doesn't violate your Fourth Amendment rights, because you do not have any reasonable expectation of privacy in your own driveway — and no reasonable expectation that the government isn't tracking your movements.

That is the bizarre — and scary — rule that now applies in California and eight other Western states. The U.S. Court of Appeals for the Ninth Circuit, which covers this vast jurisdiction, recently decided the government can monitor you in this way virtually anytime it wants — with no need for a search warrant.

read more here : http://www.time.com/time/nation/article/0,8599,2013150,00.html

One of these devices was torn down here:

Tracking Device Teardown

The crazy thing is it is totally legit.