Some months back I had discussed the game with my friend Mik who said it would involve a demon possessing different people in turn. To which I said, "if I started soon I could probably build something that will track it".
There are GPS units in the compass, the small box the demon carries and the EMF meter I later decided to build. Then packet radio to share location data. Then relays to relay the data, increasing range.
As alluded to previously I've ended up writing my own simple mesh networking protocol to make it happen. Which is quite a task, but now I've done it it'll get re-used, oh yes.