You don't even have to blow the HP-388 electronic pocket/keychain 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. Metal construction. Uses 4 LR44 batteries (included).