To activate press the black button located on the back of the necklace. Set the Light Up Blue Paw Print Charm Necklace to a fast flash, a slower blink or still light. Specifications Color: Blue Batteries: 3 replaceable AG13 batteries Height: 3.18 in. Width: 3.12 in. Depth: 1.25 in. Necklace Length: 36 in.