As far as a gps device in the car goes, that too is a breach of privacy. You might argue that the car is mine and you paid for it so you have the right to know where its going but then you are also finding out where the person is going who is driving it.

Some of the small private firms use to do it for their employees who use company vehicle and are out in the field but i have heard that, that too is illegal and they can get sued.