What Is The Difference Between An EPIRB And A PLB?

If you are considering purchasing emergency locating equipment, I am sure you will have already asked yourself: What is the difference between an EPIRB and a PLB? There is a large selection of both available to buy. But just what is the difference between the two?

The main difference is that an EPIRB is designed to be fully compliant with GMDSS carriage requirements for vessels and a PLB is not. EPIRBs are registered to a specific vessel and PLBs are registered to an individual. Aside from that, both do operate in the same way, and use the same technology to call for assistance.

What is an EPIRB?

An EPIRB is an “Emergency Position Indicating Radio Beacon”. It is designed to send a signal to satellites indicating the registered vessel is in distress.

EPIRBs meet the carriage requirements of vessels that need to comply with GMDSS regulations. One such requirement is that the battery must last long enough for 48 hours of continuous operation. This means that you know your beacon will last long enough for you to be found. This of course assumes that you have maintained the EPIRB according to manufacturers instructions and that it is in date.

EPIRBS are registered to individual vessels. Once activated, rescuers know which vessel is in distress giving them extra vital information. For example, a cruise ship will carry multiple EPIRBS. If those are activated, rescuers know the resources they send will need to be appropriate to rescue thousands of people.

When they are mounted on vessels, at least one EPIRB will be designed to float free. It will automatically activate when it comes into contact with the water. Inside, there will be a hydrostatic release, which releases the EPIRB when it comes into contact with water.

Once released, EPIRBS are designed to float in the water. All you need to do is to secure it to your liferaft and it will continually transmit a distress signal for at least 48 hours. You can set it in the water, then just focus on survival.

What is a PLB?

A PLB is a “Personal Locator Beacon”. It is designed to send signals to the same satellites indicating the registered user is in distress.

Unlike an EPIRB, PLBs do not meet the carriage requirements of GMDSS regulations. They do not have to meet specific battery life requirements, so it is up to individual manufacturers how long their batteries last.

PLBs are registered to individual people, rather than a vessel. Their personal status means they are designed to be smaller than EPIRBs, so that they can be carried easily.

To activate a PLB, you need to manually unroll the aerial and turn it on. If the user is unconscious, a PLB won’t activate automatically.

How do Locator Beacons work?

Both EPIRBs and PLBs work in the same way. Once activated they both transmit a signal on 406MHz to a constellation of satellites above the earth.

They transmit their unique code to the satellites so that the identity of the beacon is known. Some beacons also transmit their own position if they have built in GPS capabilities. If the beacon’s position is transmitted, the satellites can communicate directly with a ground station to initiate a response.

If the beacon is not equipped with GPS, further triangulation by the satellites is required to work out the beacon’s actual position.

Once detected, the distress location and identity of the beacon is sent by the satellites to ground stations. The ground stations then forward the data to the most suitable MRCC. An MRCC is a Maritime Rescue Coordination Centre, the authority who will initiate the rescue.

The MRCC can use registration databases to get all the required information about the vessel or person in distress. This will include other communication channels so that they can attempt contact, and descriptions of the vessel that they can pass on to search teams.

The MRCC will direct any maritime or aviation assets that are available towards the distress location to offer assistance. In the middle of an ocean, this will include any merchant or military vessels in the vicinity.


COSPAS-SARSAT is a system of multiple satellite constellations. The whole system receives signals from EPIRBs and PLBs on the 406MHz frequency. Each different constellation within the system serves a different purpose.

LEOSAR is a “Low Earth Orbit” constellation. This is a sequence of four satellites in a polar orbit. These satellites move relative to the surface of the Earth, so they are able to calculate the position of beacons using the Doppler effect.

GEOSAR is a “Geo-stationery Earth Orbit” constellation. These satellites are effectively fixed in position above the equator. As there is no relative movement with respect to the Earth, they cannot use the Doppler effect to locate beacons. They relay positions derived from the LEOSAR constellation to ground stations. If a beacon is equipped with GPS, these GEOSAR satellites relay the distress call directly to ground stations giving the GPS position of the beacon.

MEOSAR is a “Medium Earth Orbit” constellation. This constellation is actually made up of the satellites within the GPS, GLONASS and Galileo constellations. This is a new constellation that combines the advantages of both the GEOSAR and the LEOSAR constellations. It can use Doppler to locate beacons as well as transmitting direct GPS positions that it receives.

Homing Signal – 121.5MHz

Most EPIRBs and PLBs will transmit a second signal on a different frequency to the first. The second frequency, 121.5MHz is used as a final “homing signal” for rescuers once they are close.

The initial broadcast on 406MHz reached the satellites and directed search and rescue assets towards the distress location. Once on scene, localised signals are more effective.

SAR aircraft and vessels carry equipment that can detect the 121.5MHz frequency. This allows them to “home in” on the exact location of the beacon, saving considerable time in the final search. Especially in the case of a person in the water, even searching a few square miles could take too long.

Registration Requirements

It is a legal requirement to register all 406MHz beacons. You need to register your beacon so that search and rescue authorities know who they are searching for.

Registering an EPIRB will give rescuers specific information about the vessel that it is registered to. This could include passenger capacity, unique visual identifiers, alternative communications on board etc.

Registering a PLB will give rescuers information relating to the person it is registered to. This will include emergency contacts who should be able to give rescuers additional information about your passage plan, medical needs etc.

Failure to register a 406MHz beacon is actually an offence in most countries. Once you have gone to the expense of purchasing an EPIRB or a PLB, there really is no reason not to register it anyway.

In the US, you need to register with NOAA, and can do so at: https://beaconregistration.noaa.gov/RGDB/index

In the UK, you register with the coastguard: https://forms.dft.gov.uk/mca-sar-epirb/

Should I buy an EPIRB or a PLB?

The decision as to whether you buy an EPIRB or a PLB may be dictated by legislation. Some vessels are required to carry an EPIRB to meet their legal obligations. If this is the case, then your decision will be whether you want to carry a PLB in addition to an EPIRB or not.

I would always recommend an EPIRB is fitted to any boat that goes to sea. If mounted correctly, it will float free if you have an incident and immediately broadcast for assistance. You may get trapped in the cabin during a capsize, so having an external automatic method of broadcasting distress is invaluable.

In addition to an EPIRB, I would always recommend each crew member has a PLB fixed to themselves. The personal nature of the PLB means that it can be used if the crew member gets separated from the vessel. A typical scenario is a man overboard. Unless the person falling is spotted immediately it is very hard to locate someone in the water. Giving them the ability to call for assistance is critical for improving their chances of survival.

EPIRBs and PLBs may seem like just another expense for a mariner, but in my view the benefits certainly outweigh the cost. If it was your child going to sea, I am certain you would want them to carry both an EPIRB and a PLB. The cost of equipment is always less than the cost of a life.