This is a Dive Alert, an air horn that attaches between the BC hose and the inflator of scuba diving equipment, using air pressure to emit a sound. It is compatible with both air and H2O use. I purchased it about 10 years ago and have only used it for 20-30 dives. It has been stored at home since then. There is no salt corrosion, but some salt residue is visible in the zoomed-in photos. Please understand that this is a used item before purchasing.