Aquatec's Air3 is an innovative device that combines a power inflator, a second stage, and an air horn in one streamlined unit. Integrated with your BC, the Air3 might make an interesting replacement for that nearly-dead octopus you've been meaning to replace.
In addition to providing back-up air, the horn on the unit offers a super-charged blast (110-120 dB), and works both underwater and on the surface. Approximate surface range is about 1/2 a mile. According to the description on Amazon, on the surface, the horn sounds like a loud duck call. Underwater, the sound -- like an engine with a very bad ping -- is "more subdued but loud enough to get the attention of a buddy that has wandered off."
Expect to pay about $170 for an Air3.
