A fisherman goes overboard at night. A walker suffers a serious injury in remote terrain. A vessel develops flooding that cannot be controlled. Mobile phones, shore radio coverage and nearby assistance cannot be assumed in any of these situations.

A 406 MHz distress beacon is designed for precisely this gap. A Personal Locator Beacon (PLB) is carried by an individual. An Emergency Position Indicating Radio Beacon (EPIRB) is associated with a vessel. When correctly activated, the beacon transmits a digitally coded distress alert through the Cospas-Sarsat satellite system for processing by search-and-rescue authorities.

A PLB is small because it is intended to be carried. Its value comes from being accessible when the wearer is separated from the vessel, vehicle, group or normal means of communication.

An EPIRB is not simply a larger PLB. It is vessel emergency equipment, selected and installed around the vessel’s operating profile, approval requirements and abandonment arrangements.

An EPIRB may be held in a manual bracket or installed in a float-free housing using a hydrostatic release arrangement. Its approved programming may include vessel-related identity, depending on the protocol. That is why a change of vessel, flag, MMSI, call sign or owner cannot be treated as a paperwork detail alone.

Every 406 MHz beacon carries a programmed hexadecimal identity, commonly called the HEX ID or Unique Identifying Number—UIN.

Under current UK guidance, a first-generation beacon HEX ID contains 15 hexadecimal characters and a second-generation beacon HEX ID contains 23. The code can represent country and protocol-specific identity information, but its exact structure varies with the beacon generation and coding protocol.

The HEX ID should be found and recorded before the beacon enters service—not while someone is already trying to resolve an urgent registration or identity problem.

Depending on the manufacturer and model, the identifier may appear on the beacon’s identification label, a programming label, the product packaging, the programming report or registration paperwork. Look for HEX ID, 15 HEX ID, 23 HEX ID or UIN.

The decoder at the top of this page translates supported information from the value entered. Its purpose is clarity: to help an owner, purchaser or engineer understand the identifier without pretending that a web page has physically tested the beacon.

When an EPIRB is programmed, the service provider may create a programming report and apply an identification or programming label in the location specified by the manufacturer.

The beacon label, programming report, vessel identity and national registration record should agree. A mismatch may arise after a vessel sale, change of flag, MMSI change, reprogramming, replacement beacon or administrative error.

The satellite alert carries the beacon identity. Registration gives rescue authorities the information needed to understand who or what that identity is connected to.

For a UK registration, the owner provides the HEX ID/UIN, manufacturer, model and serial number, along with an emergency contact. Vessel registrations also require relevant vessel information. Registration is free through the UK Beacon Registry and should be updated when the owner, vessel or contact details change.

A decoder checks entered data. An engineer checks the physical beacon. The distinction matters.

IMO maintains separate guidance for annual testing and Shore-Based Maintenance of satellite EPIRBs. The applicable requirements depend on the vessel, flag administration, installation, beacon model and manufacturer instructions.

A competent test may assess the installation, housing, bracket, antenna, labels, battery expiry, hydrostatic release where fitted, transmitted message and relevant functions using suitable equipment. Shore-Based Maintenance is more extensive and can include controlled signal measurements, GNSS checks, water-contact testing, waterproof-integrity assessment and replacement of life-limited parts where required.