The Guardian Hunting Series is a line of dual-function dog collar lights used as tracking and safety lights. Waterproof, crush-proof, extremely bright and long-lasting, they will operate in flashing mode for up to 250 hours on a single battery pack. The batteries are common CR2032 coin cells, and each light includes 2 battery packs. Simply flip the battery to alternate from flashing to steady mode. This unique design was specifically engineered to lock onto the industry-standard 3/4-inch, 1-inch, or 1+1/2-inch biothane collars. They are also ideal for use on most standard 1-inch sewn nylon pet collars.