Answer to " How does the satellite know where to find me, and how exactly does it "talk" to my car? "
Although GPS communications are not bidirectional, it's virtually possible to estabilish a bidirectional communication, i.e. make the satellite "send specific data on request". The satellite actually sends data to all people around you, but if data are encrypted by a password which only your device knows, it's just like if satellite was communicating only with your device , or like if you was asking to satellite specific data.
Something similar happens on some satellite TV decoders, which can be progammed from remote by the owner although he does not own any device capable of actually sending data directly to the decoder, which can only receive data from satellite antenna: user actually connects to TV broadcaster server using standard internet connection, inform it that he wants to start his decoder at specific time, and server tell satellite to start spreading around a "start recording order" to millions of decoders around... but only one will accept the order and use it to start recording.