All satellites are constantly sending signals, but GPS devices use information from the nearest satellites to help determine your location.
GPS devices can track a device’s location in real time by using these signals from multiple satellites. Using a series of calculations and data from these signals, GPS can triangulate and pinpoint your location within 7 meters about 95 percent of the time. These signals are low-power microwave frequencies that can travel great distances, but are easily disturbed due to their weaknesses.
GPS jammer devices are designed to prevent GPS devices and satellites from stopping communication. Thus, you can prevent the GPS device from accurately calculating the location.