How's Your Dog LED Flashing Nighttime Safety Dog Collar - Midnight Black/Large (16"-19") Perfect for Walking at night - Be Seen, both you and your dog! Series of 6 L.E.D. Lights Flash Red-Blue-Yellow in a repeated sequence about every once 0.5 seconds Weatherproof, Shock Resistant and Lightweight, Visible up to 1,000 Feet Replacable Batteries (installed) - flash up to 150 hrs Available in 4 colors (Cherry Red, Parade Blue, Midnight Black and Candy Pink) and 4 sizes (S, M, L, XL)