You don't even have to blow the HP-388 electronic pocket/key-chain whistle, just push a button.
Emits a loud 120db whistle for as long as you push the button. Useful in sporting events, a locator in emergencies (earthquakes, collapsed buildings), referee whistle, traffic whistle for police, military training, dog handling and as a safety alarm for crime prevention.
4 inches long.
Uses 4 LR44 batteries (included).