To activate your LED Mouse Ears Multicolor, remove the pull tab & slide the switch on side battery house. LEDs flash a color splash combo of color change and flashing. NOTE: One size fits most. Black plastic headband is pliable, so give it a stretch or two if you’re a grown up. Dimensions (WxH): 7.5 in. x 5.75 in. LED Colors: Multicolor Comes ready to use with 2 replaceable AG13 Batteries.