sgtmnstr:
Take a look at the Mini-hammerhead, basically an air horn that fits on you LP hose works great underwater and beats the heck out of a whistle for surface emergencies. They are about $50-60 on line. It is also one less thing to secure to a d-ring because it is "in line" Rich
urgh
I have one of the "above water only" horns on my LP hose, this is much louder than the U/W type and imho as i only need this above water I want to make as much noise as possible. And it did save my Ass once when I came up from dive, the chase boat from island was waiting but they couldnt start engine, we were drifitng over the reef in shallow water with the boat nearly on top of us, i managed to make enough noise to get someone else out from the island to get us and the boat, so i am glad i bought it.
Shakers - no no no, I bought my G/f one as we were fed up with the ball on elastic tank bangers either breaking or not getting put on. She had it clipped to her b/c where it could hide in her pocket without unclipping. Only problem was every time she moved to a different angle to take photo or whatever the thing made a noise, ching ching ching ching.
Solution - Pointy sticks. About 8 inches long, 1/4" diameter stainless steel rod.
1) I can tap my tank with it to get attention of other divers
2) As a sometime dive master i can point out hard to see fish without having to stick my mits near them
3) Acts as a monopod for my video. Find a nice non living part of reef, plant one end of the stick there whilst grasping the other end and camera handle together. I can now get a nice stable video for macro, without grabbing hold of reef etc.
4) Any inamimate reef life can be prompted into action spanish dancers etc.
(the last one is a joke, please dont do that at home, saw it done once and the poor thing got speared by an urchin)