As far as I understand it, the only things a receiving device needs to work out where it is are a stable timer, a good view of the sky and time. Each satellite

As far as I understand it, the only things a receiving device needs to work out where it is are a stable timer, a good view of the sky and time. Each satellite transmits where it is and the current time in UTC, which means you can get a pretty good idea of what the time is (presumably to within a second) by picking up a single satellite's transmission, then work out what the actual time is once you've got all the other satellites and triangulated yourself. Phones can do this a lot faster by connecting to the internet to figure out what the time is, what the satellite orbital parameters are and where they all are right now. (Sources: A friend explained this to me once and I just skimmed the wikipedia page)