There is a small UV light that faces the bristles of the toothbrush when it is placed in the holder inside the case. When the lid is closed, the light comes on and begins to sterilize the brush. Within 5 minutes, the germicidal light will significantly reduce the germs on your toothbrush. The light shuts off automatically and the two AAA batteries last quite a while. The unit is lightweight and ideal for use at home, work, school, or while traveling.