On call

People could receive emergency messages on their mobile phones via an audio system — even when networks are down or out of reach, such as when underground.

Intrasonics Sound Link and Sync (SLS), developed by Cambridge's

, works by embedding data in an audio signal which can be transmitted over a radio, TV or PA system and sent using an encoded link via SLS to mobiles in the vicinity.

Rob Morland, director of Intrasonics data communications explained: 'It is essentially a way of hiding data in an audio stream. That audio can then be broadcast, stored, transmitted over TV or radio networks and played over any standard loudspeaker. It can then be picked up with the standard microphone in your mobile.'

In the event of an incident, such as on the Underground, SLS would send a further code using an audio signal from the driver's cab. this second code will activate the first, bringing up an icon on your mobile, alerting you to a message. By clicking on the link through to a remote server, the relevant message is then displayed on the screen.