2 min read · Updated 27 June 2026
An EPIRB and a PLB are distress beacons that call for rescue via satellite. When you activate one in a genuine emergency, it transmits a coded distress signal on 406 MHz to the international Cospas-Sarsat satellite network, which relays your identity and position to search and rescue authorities. They are the single most important piece of offshore safety equipment a boat carries.
EPIRB vs PLB
Both do the same core job on the same frequency, but they differ in size and registration:
- EPIRB (Emergency Position-Indicating Radio Beacon) — larger, registered to the vessel, about the size of a large water bottle. Many are mounted in a bracket to float free of a sinking boat and activate automatically.
- PLB (Personal Locator Beacon) — smaller, registered to a person, carried on the body and activated by hand. Ideal for crew who sail on different boats.
A simple way to think of it: the EPIRB stays with the boat; the PLB stays with you.
406 MHz and Cospas-Sarsat
Modern beacons transmit on 406 MHz, the frequency reserved for distress, and Cospas-Sarsat is the international satellite system that detects them. On activation, the beacon sends a digital message with its unique identity; the satellites decode it and its position and relay the alert to the right rescue authority. Since 2009, only 406 MHz beacons are detected — older analogue beacons are obsolete.
Register with AMSA
In Australia, beacons are registered with AMSA (the Australian Maritime Safety Authority), and it is free. Registration links your beacon's code to your details and emergency contacts, so when it activates, rescuers immediately know who and what they are looking for — which dramatically speeds the response. An unregistered beacon still transmits, but registration makes the rescue far more effective. (Registration details are held by AMSA; keep yours up to date.)
When to use one
A distress beacon is for grave and imminent danger — a sinking, a serious medical emergency, abandoning ship — where life is at risk and you need rescue. Activating it launches a full search and rescue response, so it is never for minor trouble. In a real emergency, turn it on and leave it on, with a clear view of the sky so the satellites can fix and track you.
Part of a layered system
A beacon works alongside the boat's other safety gear: the VHF radio for voice distress calls, the liferaft for abandoning ship, and good man overboard procedure. No single item is enough on its own. For the vocabulary, see the sailing terms glossary.
Frequently asked questions
- What is an EPIRB?
- An EPIRB — Emergency Position-Indicating Radio Beacon — is a distress beacon carried on a boat that, when activated, transmits a coded distress signal on 406 MHz to the international Cospas-Sarsat satellite system, alerting search and rescue authorities and giving them your identity and position. EPIRBs are registered to the vessel, are about the size of a large water bottle, and many are designed to float free of a sinking boat and activate automatically.
- What is the difference between an EPIRB and a PLB?
- Both are 406 MHz distress beacons that alert search and rescue via satellite, but an EPIRB is larger, registered to a vessel, and often mounted to float free and self-activate if the boat sinks, while a PLB (Personal Locator Beacon) is smaller, registered to a person, and carried on the body to be activated by hand. A PLB suits crew who sail on different boats; an EPIRB stays with the vessel.
- What is 406 MHz and Cospas-Sarsat?
- 406 MHz is the radio frequency reserved for modern distress beacons, and Cospas-Sarsat is the international satellite system that detects them. When a beacon is activated it transmits a digital distress message on 406 MHz; Cospas-Sarsat satellites pick it up, decode the beacon's unique identity and position, and relay the alert to the relevant search and rescue authority. Since 2009 only 406 MHz beacons are detected by the system.
- Do you have to register an EPIRB or PLB in Australia?
- Yes — in Australia distress beacons are registered with AMSA, the Australian Maritime Safety Authority, and registration is free. Registering links your beacon's unique code to your details and emergency contacts, so that when it activates, rescuers immediately know who and what they are looking for, which speeds up the response enormously. An unregistered beacon still transmits, but registration makes the rescue far more effective.
- When should you set off a distress beacon?
- A distress beacon is for grave and imminent danger — a genuine emergency where life is at risk and you need rescue, such as a sinking, a serious medical emergency or abandoning ship. Activating it launches a full search and rescue response, so it is not for minor problems. Once activated in a real emergency, it should be left on with a clear view of the sky so the satellites can fix and track your position.