Those in distress activate emergency beacons linked to the international Cospas Sarsat system, which picks up SOS messages via satellite and relays them to search and rescue authorities. The flashlight-sized emergency beacon transmits at 406 Mhz. This signal is picked up by participating satellites – Galileo being the single biggest contributor. Uniquely, Galileo satellites inform those in distress that their signal has been received, via their ‘Return Link Service’. The signals are relayed to regional ‘Local User Terminals’ around the globe. Four such stations were constructed as part of the Galileo system – three at the corners of Europe and a fourth in the Indian Ocean. These stations pass on the information to the nearest search and rescue site to send help. The aim is to localise an SOS call to within 2 km in 10 minutes or less. Galileo has already contributed to the saving of thousands of lives.