ASPCA Adjustable LED Safety Collars for Dogs & Cats, Three Long Lasting Blinking Options 3 lighting options: solid, slow blink, fast blink Medium: 15"-18" Includes two CR2032 Lithium Cell Batteries; up to 2000 hours Helps to keep you and your dog & other pets safe during walking Easy to use: simply pushing the control button makes the light ON/FLASH/OFF