How does a GPS know your exact location instantly?

A GPS receiver doesn't actually transmit anything - it passively listens to signals from multiple satellites orbiting Earth. Each satellite continuously broadcasts a radio signal containing its precise location and the exact time the signal was sent. Your GPS device receives signals from at least four satellites simultaneously and measures how long each signal took to arrive, since these signals travel at the speed of light. By calculating the slight time differences between signals from different satellites, the receiver uses a process called trilateration to pinpoint where in three-dimensional space you must be for all those travel times to make sense simultaneously. The fourth satellite helps correct for tiny clock errors in the receiver. The whole calculation happens in milliseconds, making it feel instant.