This is a loud dive whistle designed for use on the water's surface. This item is new and unopened, so the condition is quite good. When used in conjunction with a dive marker during ascent, such as during boat diving, it makes it easier for the boat to spot you. Those who do drift diving may feel safer having one. (※The sound does not emit underwater during diving) It is used in emergencies, when drifting, when you cannot speak due to using your tank's air, or when you want to alert someone (a boat) who is far away. When a dive alert is sounded on the surface, it can be heard from 1 mile (1.6 kilometers) away. ☆Fits all standard inflators☆ Sport Type...Diving