Emergency Position-Indicating Radio Beacons (EPIRBs) and Personal Locator Beacons (PLBs) are distress radio beacons, intended to help search and rescue teams find people or vessels in distress. They interface with Cospas-Sarsat, the international search-and-rescue satellite system, using the 406 MHz band. Most units also transmit a short-range signal on the 121.5 MHz band.

EPRIBs and PLBs notify the authorities of a crisis – not the crew aboard the vessel itself. They are therefore not the same as man overboard alarms, and should not be thought of as a substitute. Rather, MOB alarms and beacons like an EPIRB or a PLB are separate systems that are designed to increase safety in different ways.

EPIRBs signal maritime distress. Units equipped with GPS receivers are called GPIRBs. Typically, one vessel would be equipped with one or perhaps two units. All EPIRBs float, and some are activated by immersion in water.

Category I EPIRBs deploy automatically and float free if the vessel sinks; prices range from about $600 to more than $1,000. Category II units, which are manually deployed, range in price from $500 to about $800. Units of either type with internal GPS receivers cost about $200 more. Class B EPIRBs, which transmit only a 121.5-MHz homing signal, will be obsolete by Feb. 1 of 2009, when Cospas-Sarsat will stop monitoring those signals.

PLBs designed to be carried by an individual are generally for use in wilderness and other areas without access to conventional emergency services, and they are catching on in the boating world. They range in price from about $500 to $1,000, depending on features. Some PLBs include onboard GPS receivers. They are not a suitable EPIRB substitute aboard vessels heading offshore because of their limited battery life. However, portable PLBs may work well for boaters who operate exclusively in coastal waters and like to explore wilderness areas ashore.