Alfie Pet - Blauw Flashing Pet Safety Collar Please note that this listing is for the size: XS - 9"- 11" neck size (0.65" collar width). Must-have safety collar helps incoming cars and traffic see both you and your pet in the dark. Made of fiber optic and nylon fabric for maximum durability and protection from water. Lightweight and comfortable for your dog. Four modes: slow blinking, fast blinking, sustained lighting, and off. How to measure your dog's neck size: measure around the neck close to the shoulder and allow room for a comfortable fit.