Sonitus Medical of San Mateo in California has created a small device that wraps around the teeth. It picks up the sounds detected from a tiny microphone in the deaf ear and transforms them into vibrations. These then travel through the teeth and down the jawbone to the cochlea in the working ear, where they are transmitted to the brain providing stereo sound. The same process of “bone conduction” explains how we hear our own voices, and why they sound different when they are recorded and played back to us.