When diving with limited visibility or at night, it's possible to get separated from your buddy. It happens. You're chasing down a lobster in a little game of tag while your buddy is following an unusual black stingray. You turn around a minute later and he's gone. Maybe you're fishing and just speared a world-record size halibut and need a hand getting it on the stringer. In any case, you've got to get your buddy's attention.
I was taught to rap the butt end of your knife on your tank...yeah, right...as if anybody actually has the dexterity to do that gracefully within a second or two (I wear my knife on my leg). Some people actually try to yell into their regulator. Now, if it's a nice, relaxed dive, you might hear that, but if you've got a hood on or are in any sort of excited state you might not hear that.
Rodale's just did a big review on some "underwater noisemakers" that include everything from compressed air-powered horns to rattles and whistles. They recommend using the tank banger style device. They're about $8, but I can't settle for spending money on something that I can make for nothing.
I decided to create my own device out of some spare crap. I started with one of those short, fat screwdrivers (who uses those suckers anyways?). I put the handle in a vise, and using a pair of vise-grips, I twisted the driver shaft until it came out of the handle. I then drilled through the rest of the handle. Using a plastic bore drill bit (that I once used on my old guitar pedalboard), I widened the hole out. I took about 18" of extra surgical tubing (I had been using it as a slingshot in my front window) and ran it through the hole in the handle. I tied a simple knot and trimmed the excess.
To use it, you slide it around the bottom of a scuba tank. I position mine so that the handle is conveniently located right by my BC dump valve. When you're ready to make yourself heard, all you have to do is reach your hand around and "fling" the handle to make a huge CLANG against the tank. It's guaranteed to turn your buddy's head (and possibly all other divers' heads within a half mile of you).
See Thomasina's tail back there?
To order your own, send me a check for $149.95.
Sorry, no refunds or exchanges.