A Cospas-Sarsat 406-MHz beacon, also called a distress radio beacon or emergency beacon, is a radio transmitter that can be activated in a life-threatening emergency to summon assistance from government authorities.
The International Cospas-Sarsat Programme, an intergovernmental cooperative of 43 countries and agencies, maintains a network of satellites and ground facilities to receive distress signals from 406-MHz beacons and route the alerts to the proper authorities in more than 200 countries and territories. 406 MHz is the radio-frequency band in which the beacons transmit and is the band monitored around the Earth by Cospas-Sarsat.
A 406-MHz beacon designed for use in an aircraft is known as an Emergency Locator Transmitter (ELT). One designed for use aboard a marine vessel is called an Emergency Position-Indicating Radio Beacon (EPIRB). And one that is designed to be carried by an individual is known as a Personal Locator Beacon (PLB). Sometimes PLBs are carried aboard aircraft or vessels, but you must check with local authorities about the circumstances under which this is permitted. Some ELTs (often older models) transmit only a legacy analogue signal on 121.5 MHz or 243 MHz. Cospas-Sarsat does NOT monitor those frequencies and such beacons rely on being received only by nearby aircraft or rescue personnel. For satellite reception of alerts by Cospas-Sarsat the beacon must be a model that transmits at 406 MHz.
The International Cospas-Sarsat Programme does NOT manufacture, market or sell beacons. Beacons are manufactured, marketed and sold competitively by several different companies through a variety of vendor chains. A list of manufacturers is available at our Professionals website under "Contact Lists".
Beacon models are subjected to a rigorous testing procedure by Cospas-Sarsat to ensure that they will operate under a variety of extreme conditions. Once a beacon model successfully has passed this procedure it is known as a Cospas-Sarsat type-approved 406-MHz distress beacon. A list of type-approved beacon models is available on our Professionals website under "Approved Beacon Models".
A Cospas-Sarsat 406-MHz beacon does NOT transmit until it is activated in an emergency (or when certain testing features are activated by the user). Some beacons are designed to be manually activated by a person pressing a button, and some others are designed for automatic activation in certain circumstances (e.g., ELTs may be automatically activated by a physical shock, such as in a crash, and EPIRBs may be automatically activated by contact with water).
Since a Cospas-Sarsat 406-MHz beacon does not transmit until it is activated, it cannot be located by Cospas-Sarsat until after it has been activated in one of the ways explained above.