Personal Locator Beacon (PLB)

What sets a PLB apart from an EPIRB

An EPIRB is registered to a specific vessel, sized to float free or be manually launched, and built around the assumption that the ship itself is the casualty. A PLB is registered to an individual, small enough to clip onto a lifejacket or work harness, and built around the assumption that one person, not the ship, is the emergency — someone gone overboard, separated from a lifeboat, or stranded ashore during a shore excursion. Both transmit on the 406 MHz distress frequency picked up by the Cospas-Sarsat satellite system and both usually carry an integrated GPS receiver for position accuracy, but a PLB's smaller battery gives it a shorter guaranteed transmission time than a vessel EPIRB.

Main components

406 MHz transmitter

Sends a digitally coded distress burst containing the beacon's unique identity and, once GPS has a fix, an encoded position, picked up by satellites and relayed to a rescue coordination centre.

Integrated GPS receiver

Acquires position independently of any ship system, which matters because a PLB is meant to work when its owner is no longer near the vessel's own navigation equipment.

121.5 MHz homing signal

A secondary low-power beacon that search aircraft and vessels can direction-find once they are in the general area, used for final close-range homing rather than initial alerting.

Battery and activation switch

A sealed, non-rechargeable battery with a shelf life set by the manufacturer, activated manually rather than by float-free mechanism the way many EPIRBs are, since a PLB is meant to be triggered deliberately by the person wearing it.

Selection and use

Because a PLB is a personal, not statutory ship's safety equipment item on most vessels, selection usually comes down to who carries one and where: crew regularly working on deck or over the side, personnel on small work boats, and anyone doing shore-based work away from the vessel are the typical candidates. Battery replacement interval and waterproof rating deserve more attention than transmission range, since the device spends most of its life clipped to a jacket in salt spray rather than in a locker.

Regulations

PLBs operate on the same Cospas-Sarsat 406 MHz system as vessel EPIRBs and are subject to national registration requirements in the country of issue, but they are not covered by SOLAS Chapter IV distress equipment carriage requirements the way a vessel EPIRB is; a PLB is typically a company or vessel policy addition rather than a statutory fit. Registration details need updating whenever the device changes hands or the vessel or crew list changes, since an outdated registration slows down rescue coordination rather than speeding it up.

Typical faults

• Expired or dead battery — the most common failure, since PLB batteries have a fixed shelf life regardless of how often the unit is actually activated.
• Outdated registration — gives rescue coordination centres wrong vessel, contact or medical information at the moment it matters most.
• Damaged antenna or housing seal — from being clipped and unclipped repeatedly on deck, degrading transmission or letting in water.
• Accidental activation — from a worn or damaged activation switch, generating false distress alerts that erode confidence in the system.

What to look for in a supplier

• Confirmed Cospas-Sarsat type approval and current-generation coding, not an older format being phased out.
• Stated battery life and replacement interval, with the replacement battery genuinely available when needed.
• Waterproof and impact rating suited to being worn on deck, not just carried in a locker.
• Clear registration instructions and support for keeping the registration current as crew or vessel details change.

Register the PLB the day it comes aboard, not the day before an audit — an unregistered beacon still calls for help, it just tells the rescue centre nothing about who needs it.