Why do you need GPS anyway? Surest way to get your car broken into. They spot the sticker marks on the windscreen and bust the side window 'cos they know most people think they are being clever by removing the device and placing it in the glove box. Even if you put it in your pocket they'll still break into the car to try and find it.
Now these work just as well, if not better. Older technology I know but proven.