EPIRBs (Emergency Position Indicating Radio Beacons) and PLBs (Personal Locator Beacons) alert rescue services to a vessel or person in distress by transmitting signal via a satellite. This 406 MHz signal includes a unique identification code, allowing search and rescue (SAR) teams to quickly determine a vessel or person’s location. 

When an EPIRB or PLB is activated, it sends a distress signal to a satellite, which forwards it to an Earth station. From there, the information is passed to a rescue coordination centre, which will dispatch a vessel or local SAR resources to your position. 

EPIRBs can be activated manually or automatically when they come into contact with seawater. PLBs are smaller devices that are always activated manually. 

Do I need an EPIRB?

An EPIRB does not rely on there being a vessel within VHF range to hear your Mayday call, nor does it rely on somebody spotting your flares - it simply relies on the beacon being activated and functioning correctly.

For vessels regularly cruising outside reliable VHF range, a 406MHz beacon should be considered an essential piece of equipment, rather than a desirable extra, particularly for long-range cruising boats. The RYA recommends that small craft which cruise outside VHF range carry a beacon.

An EPIRB can make the difference to surviving an incident at sea even when you’re not hundreds of miles offshore or away from other vessels. For example, if you’re in a communications black spot or if you have lost VHF capability.

For occasional trips further afield than your regular cruising ground or offshore, you could consider hiring an EPIRB if you don’t want to own one or if the cost of doing so is prohibitive.

What should I buy?

EPIRBs and PLBs on the market today are dual frequency - the distress alert is transmitted on 406MHz and advises the SAR authorities of an incident, and the 121.5MHz frequency is used as an effective homing frequency, once SAR is near to the casualty.

EPIRBs

EPIRB manufacturers normally offer two types of fixing brackets for the EPIRB - manual or automatic. With a manual bracket human intervention is required to remove the EPIRB from its bracket before its activation. The automatic bracket is designed to automatically release the EPIRB from its housing as the vessel sinks. Once in contact with salt water, the EPIRB should start to transmit its emergency signal without you having to do a thing. 

The location of the EPIRB needs to be carefully thought through, especially if you decide on an automatic bracket, in which case the EPIRB must be in a position that enables it to be freely released should your boat founder, but which also affords it protection from accidental damage by crew or from being accidentally wet (or worse still washed overboard) - and prevents it from being removed or stolen when the boat is unattended. A manually activated beacon is usually either clipped on the bulkhead, just inside the companionway or is kept in the life raft grab bag.

EPIRBs are also available with integrated GPS. 

PLBs

Personal Locator Beacons are like EPIRBs but are smaller and designed to be worn by an individual crew member. Unlike EPIRBs, PLBs do not float upright and can only be activated manually. 

Like EPIRBs, PLBs are available with or without an integral GPS and once activated send the same signal via the same route as an EPIRB. With a battery life of around 24 hours, a PLB will stop transmitting before an EPIRB would.

PLBs can be used offshore, but are more likely to be chosen by users of smaller boats, RIB and personal watercraft (PWC). Carrying a PLB on your person could also be advantageous if you find yourself unexpectedly in the water - either through the boat sinking rapidly or if you have gone overboard.

Key considerations when choosing an EPIRB or PLB

When deciding whether to buy an EPIRB or PLB and what type to choose, consider: 

• the type of boating you do and the size of the boat
• the size of the equipment and how it will be stowed / carried
• with or without integral GPS (this significantly shortens the time it takes the beacon to alert the rescue service)
• the battery life (how long the beacon will transmit the signal for after it is activated)
• the operational temperature range
• manual or automatic (on contact with water) activation

There is nothing to stop you registering more than one beacon per vessel or person.

How do 406MHz beacons work?

The 406.0–406.1 MHz band is reserved solely for distress beacons that operate with satellite systems. When activated, a distress radio beacon transmits on this 406 MHz frequency. 

1. the signal it transmits is detected by instruments on board satellites in the COSPAS-SARSAT International Satellite System for Search and Rescue.
2. Local Users Terminals which are the ground receiving stations receive and process the satellite downlink signal, thereby generating distress alerts.
3. the distress alerts are passed to a Mission Control Centre which
4. relays them to the search and rescue point of contact. For a UK registered beacon this would be the Joint Rescue Co-ordination Centre in Fareham.

The signal transmitted by a distress radio beacon includes a digital message which allows the transmission of encoded data such as the unique identifier for the beacon that transmitted the alert and, if the beacon has an integral GPS, the beacon’s position. Otherwise, the beacon’s signal may need to be detected by two or three satellites before its position can be sufficiently estimated, this means it may take longer for SAR to be initiated.

The unique identifier links the beacon to the data held by the UK 406 MHz Beacon Registry about the vessel or person. This database is available 24/7 and gives the Rescue Co-ordination Centre critical information, such as the type of vessel in distress. The rescue coordination centre needs to know whether it's dealing with a cruise ship carrying thousands of people, a container ship, a fishing boat or a yacht, to know what response is needed. 

EPIRB and PLB registration 

The Merchant Shipping (EPIRB Registration) Regulations 2000, mandate registration of EPIRBs. Following a 2025 consultation, PLB registration will also soon become mandatory for use on UK flagged ships, hovercraft and watercraft. Responsibility for PLB registration will lie primarily with the PLB owner. 

In the UK, 406 MHz beacons must be registered on the UK Beacon Registry, and any changes to registered particulars also notified. Registrations and updates are free-of-charge in the UK. 

Your EPIRB or PLB must also be licensed on your Ship Radio Licence (or Ship Portable Radio Licence as applicable). 

Full details of your obligations can be found in MGN 665. 

Further information 

MGN 665 (M+F) Registration of EPIRBs and 406 MHz PLBs used in the maritime environment 

Personal emergency radio devices leaflet (explaining the differences between alerting technology and location technology)