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Distress or emergency beacons transmit a distress signal on one of two radio frequencies (406MHz or 121.5MHz). They can be high or low power and built for larger vessels offshore or for inshore personal use.

The type of distress beacon you have determines the:

  • chances of anyone receiving your distress signal
  • time it takes for anyone to receive your signal
  • accuracy of your reported position
  • information SAR services have about you.

The biggest difference between distress beacons is whether they broadcast the distress signal on 406MHz or 121.5MHz. Some distress beacons are meant to be used on boats and ships offshore; these are called emergency position indicating radio beacons - EPIRBs. Others are meant for use closer to shore on smaller craft or by divers; these are called personal locator beacons - PLBs. Make sure you get the distress beacon that suits your activities and find out if you are required to register it.


Distress beacons that operate on 406MHz send out a digital message instead of just a noise. This message includes a unique number identifying the broadcasting beacon. Providing you have registered your beacon as required, the search and rescue (SAR) emergency services will match the number to your details in a database.

They will first attempt to call you using your contact information to check it's not a false alarm. If it's not they will launch a rescue operation. The 406MHz system gives them a much more accurate idea of your position; they will also know what to look for from your registered information and will be on the way much more quickly - 406MHz beacons show up quicker than the old 121.5MHz ones.

Some 406MHz beacons have a built-in GPS, which makes the rescue even quicker; your exact position (within metres) will be broadcast along with your ID message. Rescue services will know where you are straight away (it can take up to 90 minutes to get a fix without GPS).

Distress beacons were originally designed for aircraft emergencies. The idea came about after the aircraft of two US congressmen went down over Alaska; neither they nor their aircraft have ever been found. After that, all aircraft were required to carry a distress beacon that broadcast this noise continuously in an emergency on 121.5MHz - the aircraft distress channel.

Nearby aircraft would pick up the noise and home in on it to find the casualty. Later on, satellites were also used to listen for the noise on 121.5MHz. The system also became popular on boats. Problems started to arise though; various issues with the system meant there was a huge amount of false alarms (over 90%). As there was no means of identifying who sent out the alarm, every alarm had to be checked, wasting time and resources. Also, large parts of the globe aren't covered by the 121.5MHz system, especially in the southern hemisphere.

A new system on a different frequency - 406MHz - was devised and is in use today. It fixes the problems with the 121.5MHz system and is much more effective. From 1 February 2009 satellites ceased to listen out for distress on 121.5MHz.

Distress Beacons

Emergency Position Indicating Radio Beacons EPIRBs are for use as the distress beacon for offshore vessels. EPIRBs have these important features, which PLBs don't have:

  • they must float upright on the surface
  • they must have a strobe light
  • they activate automatically when immersed in water
  • they are of a rugged construction
  • they transmit for a minimum of 48 hours.

It is VITAL that you register your EPIRB.

General maintenance

Check your EPIRB's general condition every month and perform a self-test. Follow the manufacturer's self-test instructions to the letter, to avoid sending a false alarm. Ensure your battery is replaced when required.

Using your EPIRB

Make sure the EPIRB is floating upright in the water. It may not work on its side in a liferaft. Once it's switched on, leave it on.

Accidental activation

If you accidentally activate your EPIRB inform the Coastguard. Do not switch it off until they ask you to.

PLBs - Personal Locator Beacons - are designed to locate a person rather than a vessel. They are suited to inshore use - divers, dinghy sailors and windsurfers. They are not suitable for larger craft and offshore use where an EPIRB should be used. There are two main types of PLBs:

PLBs for homing in only

Sea marshall PLB

Some just broadcast a distress sound on 121.5MHz - aircraft and rescue vessels within range can then home in on the signal to find you. They should not be relied on as a means of alerting; they just help rescue craft find you.

PLBs for homing in and alerting

McMurdo PLB

The other type could be described as a mini-EPIRB and operates on 406MHz. They alert the rescue services like an EPIRB by satellite and also help them to home in on you. This type of PLB must be registered. If you use it, try and keep it above the water and pointing upright.

Homing in

All PLBs and EPIRBs broadcast a signal that allows the SAR services to home in on your exact position. Once a lifeboat or SAR helicopter is within a few kilometres of you, a dial onboard will point to your position.

Registering your EPIRB or PLB

It it vital you register your 406MHz EPIRB or PLB with the Coastguard. The information you give when you register will help the Coastguard know what they are looking for when your EPIRB or PLB goes off. It will also help them to catch false alarms. They will use the contact details you supply to ring you if your beacon is activated.

Be sure to update your registration if any details change: this is especially important when the owner of the EPIRB or PLB changes. The Coastguard must have the new owner's details.

Get a registration form from:

The EPIRB Registry
MCA Southern Region (Falmouth)
Pendennis Point
Castle Drive
TR11 4WZ

01326 211569

Maritime Radio Affairs Unit (MRAU)
Department of Transport
Leeson Lane
Dublin 2

1890 443311