This is a Dive Alert Horn for BC/BCD Inflators. Features of this great signaling device include: Generates a blast of sound that can be heard up to a mile away The most effective and convenient surface signaling device available Connects between your low pressure hose and BC&';s Power Inflator It&';s very loud so be sure to keep it away from your ears Easy clean and rinse with fresh water after use Easy to activate red Horn Button Very compact in size The best quality components Creates loud resonating frequency Major requirement for many live-aboards and dive operations Comes in 3 models Essential piece of gear that will add to the enjoyment of your dive. Dive smart and afford to dive!