Four beacons, four different jobs

PLBs, EPIRBs, SARTs and AIS MOB beacons all exist to get you found, but they alert different people in different ways. Choose the wrong one and your alarm may reach nobody who can act on it.

The short answer: an EPIRB protects the vessel, a PLB or AIS MOB beacon protects the person, and a SART helps nearby rescuers pinpoint you during the final approach. Most offshore crews carry more than one, because each device covers a gap the others leave.

This guide explains how each one works, where it falls short, and which combination suits the way you boat. For a deeper look at a single device, read our guides on how a PLB works and on PLB registration and battery life.

PLB vs EPIRB vs SART vs AIS beacon at a glance

The biggest difference is who receives the alert: satellites and rescue centres, or vessels near you.

Device Who it alerts How it signals Protects Typical use
PLB Satellites, then a rescue coordination centre 406 MHz, often with GNSS position and a 121.5 MHz homing signal One person Offshore, solo and remote boating
EPIRB Satellites, then a rescue coordination centre 406 MHz, with 121.5 MHz homing The vessel Abandon ship, sinking, capsize
SART Nearby ships, aircraft and rescue craft AIS message (AIS SART) or radar response (radar SART) Vessel, liferaft or person Final approach location
AIS MOB beacon Vessels in range, shown on their chartplotters AIS, plus VHF DSC and 121.5 MHz on many models One person Crew overboard from a vessel

In practice these are layers, not rivals. The next four sections cover each layer in turn.

What is a PLB, and do you need one for boating?

A personal locator beacon (PLB) is a small, handheld 406 MHz transmitter that you carry or wear. According to NOAA’s SARSAT programme, PLBs are activated manually and transmit for at least 24 hours. Some units include a GNSS chip, which improves location accuracy to about 100 metres.

When you activate it, the signal goes to the Cospas-Sarsat satellite network, then to a rescue coordination centre such as the U.S. Coast Guard. Because that chain does not depend on any vessel being nearby, a PLB works far offshore, well beyond VHF range.

Do you need a PLB for boating? It depends on where and how you boat:

  • Inshore or near other traffic: an AIS MOB beacon may alert help faster, because nearby vessels see you on their chartplotters.
  • Offshore, on long passages or sailing short-handed: a 406 MHz PLB gives you a global alert path. This is the strongest case for carrying one.
  • Remote waters with little traffic: carry a PLB, ideally alongside an AIS beacon.

Carriage rules differ by vessel type and flag, so check current requirements with the U.S. Coast Guard or your national authority. Browse our personal locator beacons and S.A.R.T.s to compare 406 MHz options, including the sMRT Shield range with Return Link Service. Remember that a 406 MHz beacon must be registered; our PLB registration and battery life guide explains how.

What is an EPIRB?

An emergency position-indicating radio beacon (EPIRB) is the vessel’s distress beacon. It uses the same 406 MHz satellite system as a PLB, but it is built to be mounted on the boat and to float free when the boat goes down.

NOAA describes two categories. Category I EPIRBs can activate automatically when released from their bracket, for example when a vessel sinks. Category II units are manual-only. Both float and transmit for at least 48 hours, twice the minimum for a PLB.

Where an EPIRB falls short: it protects the vessel, not the individual. If someone goes overboard and the boat sails on, the EPIRB stays on board. That is why crews pair an EPIRB with a personal beacon on each person, such as a PLB or AIS MOB beacon.

Like a PLB, every EPIRB should be registered. The registration links the beacon’s Hex ID to you and your vessel, so rescuers know what they are looking for.

What is a SART?

A search and rescue transponder (SART) does not call for help over the horizon. Instead, it helps rescuers who are already close find you quickly. There are two types:

  • Radar SART: responds when it is struck by a ship’s or aircraft’s radar, painting a distinctive line of dots on the radar screen that points toward you.
  • AIS SART: transmits an AIS message with your position, which appears on the chartplotter or AIS display of vessels in range.

SARTs are central to SOLAS lifesaving equipment and are usually stowed for use in a liferaft or lifeboat. Our easyRESCUE is a SOLAS-approved AIS SART with an operating range of up to 15 nautical miles and 96 hours of transmission after activation. The easyRESCUE PRO adds VHF DSC.

Where a SART falls short: it only helps if a vessel or aircraft is already searching nearby. Pair it with an EPIRB or PLB so the search starts in the first place. See all options in our PLB and S.A.R.T. category.

What is an AIS MOB beacon?

An AIS man overboard (MOB) beacon is a compact device worn on a life jacket or harness. When it enters the water, or when you press it manually, it transmits your position by AIS so that vessels in range see you on their chartplotters. Many models also send a VHF DSC distress alert and a 121.5 MHz homing signal, which lets your own boat and other rescuers find you.

Why it is different from a PLB:

An AIS MOB beacon alerts vessels near you within seconds of activation, and the vessel you fell from can steer straight to your position. It is a close-range tool. Its reach depends on VHF line of sight, so it does not replace a 406 MHz satellite beacon far offshore.

Crucially, another main difference between a 406-only PLB and a beacon equipped with 121.5 MHz, AIS, or DSC is the activation method. Standard 406-only PLBs are not water-activated. In contrast, AIS and DSC models can be—and usually are—activated automatically upon water contact. We always recommend choosing a unit that is water-activated to ensure immediate transmission in an emergency.

Class M:

New AIS MOB rules, known as Class M, set a standard for how these devices behave. Our Class M FAQ explains what it means when you shop. Examples in our range include:

  • Water-activated models featuring AIS, VHF DSC, and 121.5 MHz.
  • AIS and VHF DSC Class M beacons, also offered as a bundle with a PFD.
  • “Closed loop” AIS and DSC beacons designed for inflatable PFDs.
  • ATEX Zone 1 and IECEx certified beacons for hazardous areas.

Most AIS MOB beacons are worn on a life jacket or work vest, so choose the two together.

Which beacon is best for your boating?

There is no single best PLB for boating, because the right choice depends on where you go and who is nearby. Use this table as a starting point.

Your boating Suggested setup Why
Coastal day trips near other traffic AIS MOB beacon on each life jacket Nearby vessels see you quickly
Offshore passages EPIRB on the vessel, plus a 406 MHz PLB or AIS MOB beacon per person Satellite alert plus close-range tracking
Short-handed or solo sailing AIS MOB beacon with DSC and a 406 MHz PLB Your own boat is alerted and a satellite alert goes out
Liferaft or abandon ship EPIRB and an AIS SART Global alert plus final-approach homing
Hazardous areas, offshore work ATEX or IECEx rated beacon Safe to use around flammable gas and vapour

When comparing models, check these features:

  • 406 MHz with GNSS, if you want satellite coverage
  • AIS and VHF DSC, if you want nearby vessels alerted
  • Return Link Service, which confirms the alert was received
  • Manual or automatic activation, and how it mounts to your life jacket
  • Battery standby and operating life, which we cover in our PLB battery guide

Not sure which layers you need? We offer free marine safety consulting to help you choose.

Frequently asked questions

Is a PLB the same as an EPIRB? No. Both use 406 MHz and the satellite system, but an EPIRB is mounted on the vessel and a PLB is carried by a person. EPIRBs also transmit for longer: at least 48 hours versus 24 for a PLB.

Can I use a PLB on a boat? Yes, if the model is rated for marine use. Many boaters carry one per person as a backup to the vessel’s EPIRB. Our PLB range shows which units suit marine use.

If I have an AIS MOB beacon, do I still need a PLB? Offshore, yes. An AIS MOB beacon only reaches vessels within VHF range, while a PLB reaches satellites and rescue centres anywhere.

Does a SART replace an EPIRB? No. A SART helps nearby rescuers locate you but does not start the search. See our how a PLB works guide for the satellite alert chain.

Do I need to register a PLB or EPIRB? Yes. Registration is free and required for 406 MHz beacons. Register at NOAA’s beacon registration site.

Do AIS MOB beacons use satellites? No. They use AIS and VHF radio, so they alert vessels in range, not satellites.

Build your safety layers

The safest crews layer devices: an EPIRB for the vessel, a personal beacon on every person, and a SART where regulations or the voyage call for one. Match each layer to the distance from help you are most likely to face.

Ready to choose? Browse our personal locator beacons and S.A.R.T.s, pair a beacon with a life jacket, or email is at sales@marinerescuetechnologies.com with our team.