Dual-tone whistle with no moving parts or balls that jam or corrode. A Sea-Lect, aka Sea Dog product. Handy molded clip secures the whistle to a shoulder strap, or better stowed in a life vest pocket. Expect these to come with a short length of cordage that can be clipped with a glove hook. A Sea Dog product from Sea-Lect Designs. A = 2 3/4 inches long. B = 7/8 inches wide. (Sea-Lect part # K571260-1)