If something goes badly wrong out of VHF range, a satellite distress beacon may be the only way to tell rescuers who you are and where you are. Sailors usually choose between two types: the EPIRB, which belongs to the boat, and the PLB, which belongs to a person. Both send the same kind of 406 MHz distress signal to the international Cospas-Sarsat satellite system, but they are designed for different jobs.

Quick answer: an EPIRB is a boat beacon: larger, with at least 48 hours of transmission, and in its Category I form it floats free and switches on automatically if the boat sinks. A PLB is a personal beacon: small enough to wear on a life jacket, manually activated, with at least 24 hours of transmission. For offshore sailing the best answer is usually both: an EPIRB for the boat and a PLB (or AIS MOB beacon) for each crew member on deck.

How Satellite Distress Beacons Work

EPIRBs and PLBs transmit a coded 406 MHz distress signal that is picked up by the Cospas-Sarsat system, an international network of search-and-rescue satellites in several orbits, ground stations and mission control centers. The alert is passed to the Rescue Coordination Center responsible for the area where the beacon is.

• Unique ID: every 406 MHz beacon transmits a unique identification code. If the beacon is registered, rescuers immediately know whose boat or which person it is, and who to call to confirm the emergency.
• GPS position: beacons with built-in GNSS (GPS) include an accurate position in the message, usually within about 100 meters. Older beacons without GPS rely on satellite calculations that are slower and much less precise, so choose a GPS-equipped model.
• 121.5 MHz homing: both types also transmit a low-power homing signal that aircraft and rescue vessels use to find you in the final stages of a search. Many newer beacons also include AIS, so nearby ships see you on their plotters.

A beacon is a one-way “help me” signal, not a conversation. That is why it complements, rather than replaces, a VHF radio with DSC (see how to use a marine VHF radio) and, offshore, a way to communicate by satellite.

What Is an EPIRB?

An EPIRB (Emergency Position-Indicating Radio Beacon) is registered to a vessel and mounted on board. It is larger than a PLB, floats upright with its antenna out of the water and is built to transmit for at least 48 hours. There are two categories:

• Category I: mounted in a float-free bracket with a hydrostatic release unit. If the boat sinks, the release lets go at a depth of a few meters, the EPIRB floats to the surface and starts transmitting by itself. This is the only beacon that will raise the alarm if the crew have no time to grab it.
• Category II: kept in a manual bracket. You remove it and switch it on, or it activates once it is in the water. It is cheaper and easier to keep inside, but it relies on someone taking it with them.

Mount a Category I EPIRB where it can float clear of the boat and rigging, typically on the stern rail or deck, not under a bimini or in a locker. A Category II unit should be next to the companionway, where it can be grabbed in seconds on the way to the life raft.

What Is a PLB?

A PLB (Personal Locator Beacon) is registered to a person rather than a boat. It is small enough to fit in a pocket or a life jacket pouch, must be switched on manually and is built to transmit for at least 24 hours. Because it goes wherever its owner goes, a PLB is useful on charter boats, delivery trips, other people’s yachts and ashore when hiking.

For sailors, the PLB’s main job is often a person-overboard or abandon-ship situation. Points to watch:

• Not every PLB floats, and many need to be held with the antenna upright and clear of the water to work well. Check the specifications, and choose a model designed to be mounted in a life jacket if that is how you will carry it.
• It only works if the person can reach it and switch it on, so it must be worn, not left in a bag below.
• A Cospas-Sarsat alert goes to a rescue center that may be hundreds of miles away. In a crew-overboard situation, the people best placed to help are your own crew, which is why AIS MOB beacons are worth considering too (see below).

Key Differences at a Glance

Feature	EPIRB	PLB
Registered to	The boat	A person
Minimum transmit time	48 hours	24 hours
Activation	Automatic (Category I float-free) or manual (Category II)	Manual only
Floats	Yes, upright with antenna clear	Depends on model
Size	Larger; mounted on board	Pocket-size; worn on the body or life jacket
Signal	406 MHz to Cospas-Sarsat + 121.5 MHz homing (+ AIS on many new units)	Same
Best for	Abandoning ship, sinking, offshore passages	Crew overboard, abandon ship, sailing on different boats
Relative cost	Higher, especially Category I	Lower

Which Do Sailors Need?

The right choice depends on where you sail. Always check what your national rules require: commercial and some charter vessels have mandatory beacon rules, and offshore races under the World Sailing Offshore Special Regulations specify EPIRBs and personal beacons for higher race categories.

Coastal and inshore sailing

Within reliable VHF range, a DSC radio connected to GPS, a charged handheld VHF and a phone in a waterproof pouch are the core of your distress communication. A PLB for each crew member adds a valuable layer, especially for solo sailors and anyone sailing in cold water, where time in the water is short.

Offshore and ocean passages

Offshore, an EPIRB is essential. A Category I EPIRB is the strongest choice because it works even if the boat goes down too quickly for anyone to reach it. Add a PLB or AIS MOB beacon for each person who goes on deck, worn on their life jacket together with a harness and tether. Our beginner’s guide to offshore sailing and the article on whether it is dangerous to sail around the world cover the wider safety picture.

Single-handed sailors

If you sail alone, nobody will see you fall overboard. A PLB worn at all times, ideally together with an AIS MOB device that can trigger an alarm on your own boat’s plotter or stop the autopilot on compatible systems, is strongly recommended. The best protection, though, is staying aboard: see our guide to jacklines and tethers. And if you are heading offshore, read up on heavy-weather tactics with a drogue or sea anchor.

AIS MOB Beacons and Satellite Messengers

Two other types of device are often confused with EPIRBs and PLBs:

• AIS MOB beacons transmit your position to AIS receivers and plotters within a few miles: your own boat and other vessels nearby. They don’t contact the satellite system or a rescue center directly, but they are excellent for crew-overboard recovery because they alert the people who can reach you fastest. Some units also send a DSC alert to your own radio.
• Satellite messengers and satellite phones use commercial satellite networks. Many offer two-way messaging and an SOS function that alerts a private monitoring center, which then contacts rescue authorities. They are very useful for weather, routine messages and medical advice, but they depend on a subscription and a commercial service. They are a complement to a 406 MHz beacon, not a replacement.

In a person-overboard emergency, the first priority is always to keep sight of the person and start the man overboard recovery procedure. Beacons help you find someone you have lost sight of and alert others; they don’t replace practice. A life jacket is the foundation: see our guide to the best life jackets for sailing and choose one with room for a PLB or AIS beacon.

Registration, Testing and Battery Care

Register your beacon

Registration is free and, in most countries, mandatory. It is what allows rescuers to call your emergency contacts, confirm the alert and know what kind of boat to look for.

• In the US, register with NOAA’s 406 MHz beacon registration database and renew the registration every two years, or sooner if anything changes.
• In the UK, beacons are covered by your Ofcom Ship Radio Licence and must be registered with the MCA’s beacon registry.
• Other countries have their own registries. A beacon is coded for a specific country; if you buy one abroad or move country, check that it can be recoded.

Keep the registration up to date with your boat details, emergency contacts and planned voyages. If you sell the boat or the beacon, update or transfer the registration.

Testing

• Use the beacon’s self-test function as described in the manual, typically monthly. A self-test checks the battery and circuits without sending a real alert.
• Never test by activating the beacon. Some self-tests use battery life or are limited in number; GPS tests in particular use more power, so follow the manufacturer’s guidance.

Batteries and service

• Beacon batteries have an expiry date, typically after 5 to 10 years depending on the model. Replace them by that date, or after any real use, through the manufacturer or an authorized service center.
• A Category I EPIRB’s hydrostatic release unit also has an expiry date (often two years). Check it every season.
• Inspect the bracket, the lanyard and the beacon housing for damage. Keep PLBs away from heavy objects in bags where the switch could be bumped.

If you activate a beacon by mistake

Don’t just switch it off and hope. Turn it off, then contact the Coast Guard or rescue center (by radio or phone) to tell them it was a false alert. A 406 MHz beacon sends its full message within seconds, so an alert has probably already been received.

False alerts and unregistered beacons waste search-and-rescue resources. Many incidents in real sailboat accident reports show how much a registered, GPS-equipped beacon speeds up a rescue.

Summary

• Both EPIRBs and PLBs send a 406 MHz alert to the Cospas-Sarsat satellite system; choose GPS-equipped models.
• An EPIRB belongs to the boat, transmits for at least 48 hours and, in Category I form, activates automatically if the boat sinks.
• A PLB belongs to a person, is worn on the body, transmits for at least 24 hours and must be switched on manually.
• Offshore sailors should carry an EPIRB and a personal beacon for each crew member on deck.
• Register your beacon, test it as the manufacturer recommends and replace batteries before they expire.

For a complete safety kit list, see our guide to must-have boat safety equipment for sailing.