Consider what happens when you get into you car equipped with that whizzy automated GPS tracking system, supposedly designed just to bring you emergency services when you need them. You are being tracked all the time! When your $10 WalMart sneakers (remember them - with the RF tags?)
are in your car, you are within tracking range -- they know where you are driving, to within about 20 feet, anywhere. Thanks for the bargains, WalMart!