a mechanical energy harvesting toothbrush may employ circuits and devices to convert mechanical energy into electrical energy . such conversion can be done using piezoelectric devices to convert stresses and strains from bending of the toothbrush head and / or bristles during use , and can be done using electromagnetic generators involving passing a magnet through a coil to induce current . the resulting electric energy may be rectified , and stored in a storage device , such as a capacitor or rechargeable battery . a switching circuit may be configured to detect the level of energy stored in the storage device , and to close an electrical connection when a predetermined level of energy has been reached . the predetermined level may correspond to a desired amount of brushing . the closing of the electrical connection may be used to power output devices when that desired amount of brushing has been reached .