Twenty years ago you almost certainly would have been in trouble. Rescuers might have searched for days to find you - once they even knew you were overdue.

Today the Cospas-Sarsat satellite system, set up by Russia, Canada, France and the USA in 1982, takes much of the search out of search and rescue.

A constellation of satellites quickly detects signals from emergency radio beacons and alerts search and rescue authorities around the world. Since the system became fully operational in 1985, 29 other countries, including Australia, have become involved and more than 11,000 people have been rescued. Carrying an emergency beacon means you can be certain help will be on its way when you need it.

If you activate a beacon, it starts transmitting a low-power radio signal. Satellites in geostationary and low earth orbits pick up the signal and relay it to ground receiving stations, called Local User Terminals (LUTs). The LUTs locate the beacon position and pass it to Mission Control Centres (MCCs) which coordinate the search and rescue effort (Fig.1).