Bone conduction

Bone conduction carries sound as vibration through the bones of the skull directly to the inner ear, bypassing the eardrum. In eyewear it appears in two places. As a speaker, it lets the wearer hear audio with the ear canal completely free, though the sound is thinner than a speaker moving air. As a microphone, a bone-conduction sensor picks up the vibration of the wearer’s own speech through the frame, which is why voice commands can still be understood on a windy street: the sensor hears the speaker and not the wind.