This new AQUATEC Duo-Alert is very compact in size. Only the best quality component is used in manufacturing of the AQUATEC Duo-Alert. The loud resonating frequency generated by this horn can be heard on the surface over a 1km. range, and underwater approximately 100 metres. Features: Horn works both UNDERWATER and on the SURFACE. Volume: Underwater 115-125 dB / Surface 123-130 dB. Horn is very loud, keep away from ears. Three models are available to fit of 95% of the inflators currently available. AH-380-01: Standard International connector. AH-380-02: Air 2/SS1 ScubaPro Air 2, Tusa Duo-Air and Atomic SS1. AH-380-03: Airsource Aquatec Air-3, Seaquest Airsource, Aqua-Lung Micra, Oceanic Air XS and Zeagle Octoplus.