A GPS receiver requires a direct visual connection to the satellites in order to properly receive GPS data. Tunnels, tall buildings, trees and reflective surfaces can hamper the reception or even completely block it. A metallized windshield or windshield heater can also hinder the GPS reception. In case your vehicle is equipped with such a windshield, please place your GPS receiver near the rearview mirror. Car manufacturers usually spare this area from applying additional layers in order to be able to install transmitters for garage door openers here. Many receivers or mobile devices can also be equipped with an additional external GPS antenna.