Behind the ear gesture control for a head mountable device

A head-mountable device (HMD) comprising:

• a microphone;
• a frame having an earpiece portion configured to be located proximate an ear of a wearer when the HMD is worn;
• a gesture-detection sensor located in the earpiece portion, wherein the gesture-detection sensor is configured to detect a first gesture and a second gesture in a buttonless-touch region located posterior to the ear of the wearer;
• and
• a processor configured to:
• activate a voice interface responsive to a first signal from the gesture-detection sensor indicating that the gesture-detection sensor detected the first gesture in the buttonless-touch region located posterior to the ear,
• receive an audio input signal from the microphone while the voice interface is activated,
• after the first signal is received, deactivate the voice interface responsive to a second signal from the gesture-detection sensor indicating that the gesture-detection sensor detected the second gesture in the buttonless-touch region located posterior to the ear, and
• determine a voice command based on the first signal, the second signal, and the audio input signal, the voice command having a start-point that corresponds to the detected first gesture and an end-point that corresponds to the detected second gesture,
• wherein the first signal indicates that a finger is positioned and held in the buttonless-touch region to the posterior to the ear and the second signal indicates that the finger is removed from the buttonless-touch region to the posterior to the ear.