To activate your LED Mouse Ears, remove the pull tab & slide the switch on side battery house. LEDs glow a steady light, no flash. NOTE: One size fits most. Black plastic headband is pliable, so give it a stretch or 2 if you're a grown up. Dimensions (WxH): 7.5 in. x 5.75 in. LED Colors: 2 Blue Ears come ready to use with 2 replaceable AG13 Batteries.