This tracker is the industry standard for beacons. Most cat/heli operations use these. In essence, when the beacon is in transmit mode, it sends a signal as to its location. Each beacon can also be switched to "search" mode to look for other beacons that are in the transmit mode. They're useful in that, if you have 2 or more people backcountry skiing, it enables one to search for the other if he/she is taken down in an avalanche and buried. They are absolutely essential to backcountry skiing.