EPIRB vs PLB vs AIS MOB: Which Emergency Beacon Should You Carry?

Choosing between an EPIRB, a PLB, and an AIS MOB beacon is not a matter of buying the most expensive unit or the one with the longest battery life. Each device talks to a different network, alerts a different audience, and is optimized for a different rescue scenario. An EPIRB is registered to the vessel and calls the global Cospas-Sarsat satellite system. A PLB is registered to a person and does the same from a pocket or lifejacket. An AIS MOB beacon broadcasts a local alarm to nearby AIS-equipped vessels. The right choice depends on where you sail, who is aboard, and how quickly you can expect help.

Main Explanation

What it is

EPIRB, PLB, and AIS MOB are three distinct types of emergency beacons used in recreational sailing. They are not interchangeable, and the decision framework here treats them as complementary layers rather than competing products. An EPIRB (Emergency Position Indicating Radio Beacon) is registered to a specific vessel and is designed to stay with the boat. It transmits a 406 MHz distress signal via the Cospas-Sarsat satellite network, which relays the alert to search and rescue (SAR) authorities anywhere in the world. EPIRBs come in Category I (automatic, float-free deployment) and Category II (manual activation). A PLB (Personal Locator Beacon) is registered to an individual, not a vessel. It is smaller, can be carried in a pocket or attached to a lifejacket, and also uses the 406 MHz Cospas-Sarsat satellite system. An AIS MOB (Automatic Identification System Man Overboard) beacon is different: it does not use satellites. Instead, it transmits a distress alert and GPS position on AIS frequencies to nearby AIS-equipped vessels and chartplotters, typically within 1 to 2 miles. According to Oria Marine, only two of the three talk to satellites, and only one is designed to stay with the boat.

Why it matters

The wrong beacon choice can delay rescue by minutes or hours, and in cold water or rough seas that delay can be fatal. Oria Marine describes the three devices as ‘three networks, three very different rescues.’ West Marine calls EPIRBs and PLBs ‘life insurance that we hope you’ll never need to use.’ The challenge for recreational sailors is that information is scattered across manufacturer manuals, forums, and outdated advice. A sailor who equips a coastal daysailer with only an EPIRB may have no fast way to alert the boat if a crewmate goes overboard. A sailor who carries only an AIS MOB on a solo offshore passage may find that no nearby vessel receives the alert. Matching the beacon to how, where, and with whom you actually sail is the core of the decision.

How it works

EPIRBs and PLBs share the same satellite backbone. When activated, they broadcast a 406 MHz signal to Cospas-Sarsat satellites. If the unit has GPS, the position is included in the first transmission; without GPS, the system triangulates the signal to within about two nautical miles, and notification can take up to about one hour, according to West Marine. The alert is routed to a national SAR authority, which then coordinates a response. EPIRBs are mounted in a bracket or float-free housing; Category I units deploy automatically if the vessel sinks. PLBs require manual activation and a clear view of the sky. Both must be registered with the appropriate national authority, and the registration must be kept current.

AIS MOB beacons work locally. They transmit on AIS frequencies and appear as a man-overboard symbol on any AIS receiver or chartplotter within range, typically 1 to 2 miles, though some sources cite up to 5 nautical miles under ideal conditions. They can be activated manually or automatically when an inflatable lifejacket inflates. Ocean Signal notes that AIS MOB beacons are ideal for coastal boating and crewed sailing because the boat itself is usually the nearest rescue asset. They do not alert SAR authorities or satellites.

How to do it

To choose the right beacon, start with a realistic assessment of your sailing profile. For a coastal day sailor with crew, the primary man-overboard risk is best covered by an AIS MOB beacon on each lifejacket, backed up by a VHF DSC radio and an EPIRB on the boat. For an offshore cruiser, an EPIRB mounted on the vessel is the first line of defense for abandoning ship, while a PLB on each crewmember’s lifejacket provides a personal satellite alert if separated from the boat. For a solo offshore sailor, a PLB is essential, but an EPIRB on the boat and a satellite messenger for two-way communication add redundancy. After selecting the type, check integration: AIS MOB requires an AIS receiver or plotter; EPIRB requires proper mounting and registration; PLB requires accessible stowage. Register the beacon, test it monthly, and practice activation with the whole crew.

When not to do it

Do not rely solely on an AIS MOB beacon for offshore or solo sailing, because its range is limited to nearby vessels and it does not reach satellites. Do not rely on a PLB as the primary vessel distress alert if the boat is sinking and you cannot activate it before abandoning; an EPIRB should be mounted on the boat. Do not treat any beacon as a substitute for a VHF DSC radio, visual distress signals, or professional training. A beacon is a last-resort alerting device, not a communication tool. If you need to talk to rescuers, coordinate with nearby vessels, or receive weather updates, you need additional equipment. Finally, do not use a beacon that is unregistered, has an expired battery, or has not been tested.

Visual

The table below compares the three beacon types with VHF DSC and flares as complementary emergency signaling sources.

Common Mistakes

Assuming an AIS MOB beacon calls the global rescue system

Many sailors believe that any beacon with ‘MOB’ in the name will summon satellites and SAR authorities. In reality, an AIS MOB beacon only broadcasts to nearby AIS-equipped vessels within about 1 to 2 miles. If no vessel is in range, no one receives the alert. The consequence is a false sense of security, especially offshore. The correct approach is to pair an AIS MOB with a PLB or EPIRB for satellite alerting when sailing beyond coastal traffic.

Carrying an EPIRB but never registering it or updating the registration

An unregistered EPIRB still transmits, but SAR authorities have no information about the vessel, owner, or emergency contacts. This can delay the response and complicate identification. Registration is free in most countries and must be updated when the boat changes hands or contact details change. The correct approach is to register the beacon immediately after purchase and review the registration annually.

Using a PLB as the only man-overboard alert on a crewed coastal boat

A PLB alerts satellites and SAR, but the response may take many minutes or longer. On a crewed coastal boat, the fastest rescue asset is the boat itself. An AIS MOB beacon gives the crew an immediate position on the chartplotter, allowing them to turn around and recover the person quickly. Relying only on a PLB can mean the crew loses sight of the victim while waiting for outside help. The correct approach is to use AIS MOB for local recovery and a PLB as backup.

Ignoring battery expiry dates and self-test routines

Beacons have a finite battery life, typically around five years for EPIRBs and PLBs. A beacon with an expired battery may fail when activated. Self-tests can catch faults, but they are often skipped. The consequence is a false sense of security and a dead beacon in an emergency. The correct approach is to follow the manufacturer’s self-test schedule, replace batteries before expiry, and log the tests.

Stowing the beacon where it cannot be reached in an emergency

An EPIRB mounted in a locker or a PLB buried in a ditch bag is useless if you cannot reach it when the boat is sinking or someone is overboard. The consequence is lost time and possibly lost access. The correct approach is to mount the EPIRB in an accessible, float-free location and keep PLBs on lifejackets or in dedicated pockets that can be reached with one hand.

Treating a beacon as a substitute for VHF, visual signals, and training

A beacon is a one-way alert. It does not let you talk to rescuers, coordinate with nearby vessels, or signal your exact position visually. Relying on it alone leaves gaps in communication and recovery. The correct approach is to carry a VHF DSC radio, flares, a signal mirror, and to take a certified safety and sea survival course so that you know how to use all the tools together.

Safety Note

Emergency beacons are one layer in a broader safety framework, not a replacement for seamanship, training, or human judgment. Always cross-check critical data such as weather, tides, and navigation with official sources; do not rely on a single app or device. Keep paper charts and a handheld compass as backup, and never use a phone or tablet as your only navigation tool. Take a certified safety and sea survival course, and practice man-overboard recovery and beacon activation with your crew. Register your EPIRB or PLB with the appropriate national authority and keep the registration current. Test beacons according to the manufacturer’s instructions and replace batteries before expiry. Follow the International Regulations for Preventing Collisions at Sea (COLREGS) and all local maritime regulations regarding distress signals and safety equipment. A beacon can call for help, but only a well-prepared crew can survive long enough to be rescued.