They use cell service or sat phone or some kind of sat service like GlobalStar. And they're suggestively called trackers, so there is no expectation of privacy.

They use cell service or sat phone or some kind of sat service like GlobalStar. And they're suggestively called trackers, so there is no expectation of privacy. GNSS receivers are passive devices just like regular radio receivers, but in addition to regular radios they use math to process the deltas from GNSS satellite clock signals to pinpoint their position.