This is the Dive Alert PLUS v2 Signaling Device Power Whistle Safety System

Features:

• The DiveAlertPLUS uses chrome-plated brass couplings to attach to your power inflator
• Squeezing the device engages the actuator valve stem causing a small amount of air to
  flutter a stainless steel diaphragm, emitting a piercingly loud sound from the injection-
  molded thermoplastic body
• The subsurface/underwater signal is produced by a percussion buzzing" noise made by
  a piston hitting a stainless steel diaphragm much like a drum
• Body and Internal Elements:Injection-molded Thermoplastic
• Diaphragms: Stainless Steel
• Couplings: Chrome-plated Brass
• DV1 Fits all Standard Inflators
• DV2 fits SeaQuest AirSource 1&2, Zeagle Octo-Plus, Oceanic Air XS & MARES AirControl AirSource 3 QD
• DV3 fits ScubaPro Air 2, Tusa Duo-Air Atomic SS1, Sherwood Gemini, and Zeagle Octo-Z
One Year limited Warranty

DiveAlertPLUS is a specially designed, small, light weight pneumatic signaling device that uses quick-connect/disconnect hose couplings to become an integrated part of your power inflator. Installation is easy and takes only a moment. DiveAlertPLUS uses a small amount of air from your SCUBA tank to make a piercingly loud sound in air or water. People have been able to hear a DiveAlertPLUS one mile away from a diver in need above water. In conditions where visibility is limited, a DiveAlertPLUS can be a life saver. Underwater you can sound for attention quickly with a squeeze of the device.