Emergency beacons are of two types: emergency, position-indicating radio beacons (EPIRBs) that signal a boat in distress and personal locator beacons (PLBs) that signal a person in distress who cannot contact local emergency services such as 911. All EPIRBs today send to orbiting satellites a 406-MHz digital signal, which identifies the unit and might also include GPS coordinates. Some also send a 121.5-MHz analog homing signal that most aircraft can monitor. Older units that do not operate at 406 MHz are obsolete and should be discarded. Two types of EPIRB are Category I, mainly for commercial use, which floats free of its mount automatically and is water activated, or Category II, which is manually deployed and might also be manually activated. Two classes of EPIRB are Class 1, good down to -40°C and Class II, good down to -20°C. Every EPIRB must be registered with NOAA, once every two years, and should be tested biannually by a professional.
