Safety kit
What Is an EPIRB? Emergency Beacons for Boats Explained
Published · Last checked October 2026
An EPIRB (Emergency Position Indicating Radio Beacon) is a distress beacon registered to a boat. When activated, manually or automatically when it floats free, it transmits on 406 MHz to the Cospas-Sarsat satellite system, which passes your identity and GPS position to rescue services. It also sends a 121.5 MHz homing signal so lifeboats and helicopters can find you. In the UK, register it free with the UK Beacon Registry. It is the boat's last-resort alert when VHF is out of range or not working.
How it works
- The beacon is activated by hand, or by water contact if it floats free from its bracket.
- It sends a coded 406 MHz signal with its unique ID (and GPS position if fitted).
- Cospas-Sarsat satellites pick it up and relay it to ground stations.
- The alert goes to the rescue coordination centre responsible, which checks the registration and launches search and rescue.
- A 121.5 MHz homing signal and strobe light guide rescuers in the final stages.
Types of EPIRB
| Type | How it activates | Typical use |
|---|---|---|
| Category I | Hydrostatic release frees it from the bracket if the boat sinks; floats up and switches on | Offshore yachts and commercial vessels |
| Category II | Manual release from bracket; water-activated or manual switch | Coastal and offshore yachts where crew grab it |
| AIS-enabled | Also transmits on AIS so nearby vessels see the alert | Modern beacons |
EPIRBs are designed to transmit for at least 48 hours. Batteries have a replacement date, commonly around 5 to 10 years, and the hydrostatic release on a Category I unit typically needs replacing every two years.
Registration and testing
- Register the beacon free with the UK Beacon Registry (run by the MCA) and update it when you change boats or contacts.
- Use the self-test function as the manual describes. It does not send a live alert.
- Check the battery and hydrostatic release expiry dates each season.
- If you set it off by accident, call the coastguard to say so. Do not just switch it off and hope.
EPIRB or PLB?
An EPIRB is registered to a vessel and has a longer battery life. A PLB is registered to a person and is small enough to wear on a lifejacket. Many offshore crews carry both. The safety equipment lesson and abandon ship lesson cover when to deploy them.