To activate the the HP-388 electronic pocket/keychain whistle alarm all you have to do is push and hold on the button. For as long as you hold the trigger it will a emit an ear piercing 120db whistle sound alarm. Some common uses are: referees, emergency locator, traffic whistle, military training, dog handling, and of course a safety personal alarm to deter crime.

This whistle alarm is 4 inches long, is constructed of metal and uses 4 LR44 batteries (included).