Distress radiobeacons, also known as emergency beacons, PLBs (personnel beacon), ELTs (aircraft beacon), or EPIRBs (maritime beacon), are location transmitters utilized to determine the location of boats, aircraft, and people. These devices emit a radio signal that is tracked strictly by the Cospas-Sarsat search and rescue satellite program, which was established in 1979 by the U.S., Canada, France, and the U.S.S.R. When the devices activate, either manually or upon liquid emersion, a signal is transmitted to a local user terminal where individuals can determine the beacon's location by either doppler or GPS triangulation. A regional rescue operations center then responds to this information. These distress beacons are almost exclusively restricted to travel in remote locations, and are discouraged in locations where typical emergency response infrastructure exists.
Image credit: Wikimedia