Special - a 406Mhz beacon is what you are talking about and they send a databurst transmission every 50 seconds or so in two hexadecimalgroups. One has the identity of the beacon (they are required to be registered) and the second has the GPS position in it. They also transmit a continuous 121.5 tone.
It isn't triangulation - that is what the old satellite system used and it could give large errors.
The data is downloaded to an earth station (Land User Terminal) when the satellite is in view of it.
Lowfat - yes, in that case the'smart' beacons from the aircraft didn't transmit because they recognised an apparent stronger signal (the wrist beacons) and didn't operate properly.