The Emergency Position Indicating Radio Beacon (EPIRB) provides the simplest way of alerting the rescue authorities. EPIRB's are ‘transmit only’ devices and transmission is limited to the pre-programmed function.

There is no facility for spoken communications.

The most common EPIRB system is operated on 406 MHz by the COSPAS/SARSAT organisation which uses polar orbiting satellites.

If a vessel sinks the 406 MHz EPIRB is designed to detach itself automatically, float free and transmit a distress signal via the satellite system. Using the signal the position of the casualty is calculated——to within about three nautical miles—and the information relayed to the nearest Rescue Co-ordination Centre.

406 MHz EPIRB's also transmit a signal on 121.5 MHz which enables search and rescue vessels to obtain a radio bearing of the EPIRB.

The 406 MHz EPIRB will transmit an identity, either in the form of a serial number or the ship’s own identity (call sign). The serial number can be checked against a register to determine to which vessel the particular EPIRB has been assigned. Thus a distress signal received from a 406 MHz EPIRB enables the rescue organisations to determine exactly which vessel is involved—and so at least gain a close approximation of the number of persons involved—and the exact position. EPIRB registration details include the name, type, call sign and MMSI of the vessel, maximum number of persons carried, and details of the owners.

Some EPIRB's incorporate a GPS (Global Positioning System) component which additionally transmits a latitude and longitude position, updated every twenty minutes.

Some older EPIRB's used the aircraft distress frequencies of 121.5 and 243 MHz, but required an over-flying aircraft before detection. Some personal EPIRB's transmit only on the aircraft and regional mode SARSAT/COSPAS frequency 121.5 MHz.

EPIRB's require little maintenance, except to check their operation by use of the ’test’ function, and to

renew the battery and the hydrostatic release mechanism (if fitted) at intervals as prescribed by the manufacturer.