These Light Up LED Pet Collars are great for locating your pet in the dark and also provide safety for your dogs and pets while they are out alone at night. The Light Up LED Pet Collars come in Small or Medium, with the color option of Red or Blue. Small measures: 16"L by 1"W. Medium measures: 17. 5" L by 1" W. All collars are battery replaceable, simply push out the area where the button is located and pop open the box and replace the batteries. They are very easy to use: simply push the control button and it makes the light turn on and flash rapidly, click again and it begins to flash slowly, click again and the light stays on without flashing. Click once more to shut off light. Get your Light Up LED Pet Collar now and keep your pet safer with this simple product. Each collar takes (2) CR2032 Lithium Cell 3V batteries. (Batteries included).