jp27 wrote an answer about Ortovox F1 Focus Avalanche Beacon on January 16, 2010
All beacons work on the same frequency, but over time transceivers can begin to have their frequency change. Basically there is a crystal that is inside that dictates the frequency. All transceivers have to be within a certain frequency range to be able to be sold. (I think 10-15 kHz) Pieps makes one that can check to make sure that the frequency range is adequate, no matter who makes the transceiver. That is, if I have a Pieps I can check all the people I am skiing with to be sure their transceivers, no matter who makes it. This is especially useful if you are with someone who has an older transceiver.