Definition:

PLBs, officially known as Personal Locator Beacons, are small, personal emergency beacons used to notify search and rescue agencies of distress. They are designed to save your life if you get into trouble by alerting rescue authorities and indicating your location anywhere in the world. They utilize the COSPAS-SARSAT and GEOSAR satellite systems by sending a distress signal on 406 MHz frequency that is used to pinpoint your exact location.

The coordinates are then sent to the appropriate agency to begin rescue efforts. PLBs can also be equipped with GPS technology that transmits your LAT/LONG for precise locating and faster rescue.

Further reading about EPIRBS and Personal Locator Beacons (PLBs):

EPIRBs

What Exactly is an EPIRB?

How EPIRBS Work

How to Register an EPIRB or PLB

The Best EPIRB or PLB to Buy

Marine Electronics Review - SPOT Personal Locator Beacon

Marine Electronics Review - ACR Electronics AquaFix 406 I/O Personal Locator Beacon

Marine Electronics Review - ACR Electronics ResQFix 406 GPS Personal Locator Beacon

Marine Electronics Review - ACR Electronics GlobalFix iPRO EPIRB

Also Known As: Emergency Position Indicating Radio Beacon, Personal EPIRB, PLB, Personal Locator Beacon, Emergency Beacon, 406 MHz Beacon