Basic Tank Banger is Simple, Economical, and Effective
Making noise under water doesn't get any simpler than this. The elastic band is made of surgical tubing that is fitted with a hard plastic ball.
Stretch the band over your scuba tank. When you want to get your buddy's attention, simply reach back, grab hold of the ball, pull it away from the tank and let it go. The clang is sure to turn heads.
