Avalanche transceivers are small devices that transmit and receive a radio signal from another transceiver. When traveling in avalanche terrain, everyone has a transceiver on in transmit mode. In the event that an avalanche catches someone in the party, those that are not buried then switch over their beacons to receive and locate their buried friend. It takes practice, practice and more practice to reliably conduct a beacon search on an avalanche debris pile. Speed is absolutely critical when searching for a buried victim.
Fresh batteries are also essential.
Remember this if you rent or borrow a beacon and always put in your own fresh batteries. A major shift in avalanche transceivers occurred several years ago when all new models were switched to a higher single frequency of 457 kHz. Be sure to check this out with new hiking partners before starting your trip. If you have not retired your old low frequency beacon, do so now. Another major change now underway is the advent of digital beacons.