PLB (or Personal locator beacons) and EPIRBs (Emergency Position Indicating Radio Beacons) are used to alert search and rescue teams and services of your location in event of an emergency. Both transmit a coded message over the 406MHz frequency -- which is reserved exclusively for distress calls -- to the closest rescue centre. PLBs are registered to a person and are generally smaller, and it's battery will usually last for 24 hours. EPIRBs are registered to a vessel and transmit an emergency signal for around 48 hours and thus if you buy a new boat you'll need a new EPIRB. For more information or advice call 01634 295 233.