Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A biofeedback headband is a self-contained biofeedback unit which is worn on the head and held in place by an elastic strap. Biofeedback headbands are most often used for controlling bruxism during sleep, but can also be used during the day. Clenching is sensed through electromyography (EMG) by picking up microvolt-level muscle signals from the temporalis muscles through black conductive rubber sensor pads which contact the user's forehead and temples when the unit is worn. Modern biofeedback headbands track clenching and grinding activity as well as providing biofeedback. After a night of use, the user can read out of the unit both the number of clenching incidents detected, and the total amount of clenching time accumulated through the night. Biofeedback headbands may also be used to reduce tension headaches and migraines which are caused when bruxism or excessive tightening of frontalis muscle.