Emergency position indicating radio beacons - EPIRB

  An epirb is a small electronic device that can help search and rescue authorities find people in distress.          When activated, it emits a continuous distinctive radio distress signal for at least 48 hours. You should            only use an EPIRB when there is grave and imminent danger.

  During an emergency, you should first try to communicate with others by using radios, phones and other        signalling devices. Mobile phones can be used but should not be relied on as they can be out of range,          have low batteries or become water-damaged. 

Excerp from www.sa.gov.au