It has happened to almost everyone. You are sitting on a train or a bus and someone right next to you is annoyingly shouting into his or her mobile phone.

But those days could soon be past with "silent sounds", a new technology unveiled at the CeBIT fair on Tuesday that transforms lip movements into a computer-generated voice for the listener at the other end of the phone.

The device, developed by the Karlsruhe Institute of Technology (KIT), uses electromyography, monitoring tiny muscular movements that occur when we speak and converting them into electrical pulses that can then be turned into speech, without a sound uttered.

"We currently use electrodes which are glued to the skin. In the future, such electrodes might for example by incorporated into cell phones," said Michael Wand, from the KIT.

The technology opens up a host of applications, from helping people who have lost their voice due to illness or accident to telling a trusted friend your PIN number over the phone without anyone eavesdropping — assuming no lip-readers are around.