Our Blue LED Safety Light for Pet Collars will keep your pooches safe at night. Let them roam the park with you after dark and never lose sight with these flashing multicolor safety lights. To activate your safety light, attach the carabiner to your dog's collar then twist the head of the light clockwise until it is tight and alight. One light mode: Flashing. LED Safety Light for Pet Collars comes ready to use with 3 replaceable AG3 Batteries.