To add to what Tjin said.
Avalanche beacons are also avalanche beacon receivers.
If you dissapear under a cloud of the white stuff, your friends switch their beacons to search mode and look for you. this of course requires training (and a certain level of inteligence) - having just the one beacon is pretty pointless.
Although some resort and mountain resuce groups have avalanche beacons that can be carried by helicoter to search a large avalanche area quickly - this is really only useful if one hits a ski run where they know there are people.

There are also cheap passive avalanche beacons (RECO tags) which can be built into clothes and ski gear. These are very short range, the rescuer has to be prety much standing over the top of you. They are standard for all skiers and ski patrols in european resorts but seem rare in the US.