Emergency Position Indicating Rescue Beacon (EPIRB)
An essential item when ocean cruising, a satellite beacon is intended for your boat, rather than for personal use. It is usually automatically activated on contact with water, when it repeatedly transmits a distress call on 406MHz to the COSPAS/SARSAT worldwide rescue authorities.
An EPIRB must be registered to a particular vessel and details left on file to assist the authorities with the search if ever required. The main advantage they have over a PLB is that they have larger battery pack so they can transmit for longer (minimum 48 hours).