The Arcturus LED dog collar by AVS, Inc. will Improve Nighttime Visibility for your dog and provide you with peace of mind knowing that others, including drivers can easily see your dog when walking at night. All of our collars are made of sturdy nylon, fluorescence webbing with a very bright LED optic fiber in the collar. It comes in an array of bright colors including red, orange, yellow, green, blue and pink. You will get about 50 hours of steady light; although if left on continuously it will begin to dim after 36 hours or so. With normal use the battery should last you several months. You can choose from two flashing speeds and one steady light speed. All batteries in each collar are replaceable. Replacement batteries are CR2032 button battery. . The Arcturus LED Light-UP Dog Collar is stylish, durable, light-weight, flexible, easy to store, and fun to use. But more importantly it can save your dog's life. Get one for each of your dogs today. Makes a great gift for any dog-lover. Untold numbers of dogs are struck and injured and/or killed by vehicles every year. The Arcturus LED collar will minimize the possibility of this catastrophe from happening to your beloved family friend. Measure your dogs neck and add about 2 inches and pick the size you need: Small - Width 1 Inch, length 11-14 inches Medium -Width 1 Inch, length 14-18 inches Large - Width 1 Inch, length 14-21 inches.