Short · Space
How does GPS know where you are?
Your phone never sends anything to the satellites. It times each signal from their atomic clocks, and four distances, one of them fixing the phone's own clock, pin down your position.
Try it yourself
Opens GPS Lab. Change the same thing yourself.
Transcript
How does GPS know where you are? Your phone doesn't send anything to the satellites. It only listens. Each satellite broadcasts the time from an atomic clock, and the signal takes about seven hundredths of a second to fall twenty thousand kilometers. That delay gives the distance. Now add satellites. Three distances meet at one point, and a fourth corrects your phone's own clock. Off by a millionth of a second, you'd be three hundred meters off. Try it yourself at Explainer Tools dot com.