Personal Locator Beacons
Distress radio beacons, also known as emergency beacons, PLB (Personal Locator Beacon), ELT (Emergency Locator Transmitter) or EPIRB (Emergency Position-Indicating Radio Beacon), are tracking transmitters which aid in the detection and location of boats, aircraft, and people in distress.
Strictly, they are radio beacons that interface with the worldwide offered service of Cospas-Sarsat, the international satellite system for search and rescue (SAR).
When manually activated, or automatically activated upon immersion, such beacons send out a distress signal. The signals are monitored worldwide and the location of the distress is detected by non-geostationary satellites, and can be located by GPS trilateration and doppler triangulation.
Since the inception of Cospas-Sarsat in 1982, distress radio beacons have assisted in the rescue of over 28,000 people in more than 7,000 distress situations. In 2010 alone, the system provided information which was used to rescue 2,388 persons in 641 distress situations.