The nite ize led carabiner light has a very robust watertight electric led with a rust free carabiner you can securely attach the round tag to your dogs collar and set the light to steady or flashing status this makes your dog visible in the dark from a distance of up to 300m it runs on typical 3v cr 2032 batteries and lasts approx 150 hours changing batteries with a phillips screwdriver is easy as pie led settings on press down on the marked button for 2 seconds flashing press down o