there is an LED strip in it that lights up when u push the button. Im only selling it because I bought it and it is too big for my puppy. It is brand new never worn.
It requires Battery: 2PCS CR2032 button batteries. Right now I dont have the right battery in it. It fits but just doesnt stay on unless u keep ur finger on the button, if u put in the right batteries, it will stay on when the button is pushed.