and see the nice little FAQ they have. http://www.arb.ca.gov/html/coolcarsfaq.pdf Will my GPS still work? Yes. Many automobile manufacturers currently equip their vehicles with external antennas to ensure proper functioning of factory installed GPS devices. For aftermarket GPS devices, deletion windows, or areas without reflective coatings, will be created in the windshield and the location of these windows noted in the owner’s manual. ARB tests showed that placing the GPS device or the external antenna within the deletion window allows the device to operate as effectively as in a car with no reflective glass.

obligatory quote: Arguing on the internet is like running in the Special Olympics. Even if you win, you're still retarded.