SPOT sends a signal giving position every ten minutes if switched on. (At least mine does.) Also has an emergency button and also a regular message button which sends a pre recorded message (ie. Safely arrived way point,xxx) but it only does one message until re-recorded.
Local flying schjool here has been usong them for years now but recently uses something else similar. Haven't enquired why, (Maybe cheaper or more effective.)
There was a move here to allow SPOTs instead of emergency beacons as the new frequency beacons are rather expensive but it was turned down.
Should be used by hikers and ski tourers. It would make finding them a lot simpler. Maybe if you are in a club or group you could share one too, though it is not that expensive in flying terms.