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. (See a TIME photoessay on Cannabis Culture.)
The court went on to make a second terrible decision about privacy: that once a GPS device has been planted, the government is free to use it to track people without getting a warrant. There is a major battle under way in the federal and state courts over this issue, and the stakes are high. After all, if government agents can track people with secretly planted GPS devices virtually anytime they want, without having to go to a court for a warrant, we are one step closer to a classic police state - with technology taking on the role of the KGB or the East German Stasi.