The message contains at least the ship's position and identity, plus time of the emergency. Operators may also send additional information about the type of emergency. Weather conditions and other users do not affect L-band reception. The satellites relay the data to an Inmarsat ground station which triggers the alert, simultaneously sending information via landline to a Rescue Coordination Centre. Once triggered, terminals continue transmitting for 48 hours unless manually shut off.
Some models contain an additional radar beacon to aid rescuers.
Inmarsat is negotiating for a fourth station for the Atlantic. But in fact, even now with three stations operating, there is only one small section of the Pacific without double coverage. Inmarsat began operation in 1982, providing satellite communications to customers around the world.