The COMPACT ELECTRONIC POCKET WHISTLE blows itself with a push of a button. This whistle emits an ear shattering 120 decibel whistle for as long as you hold the button. This can be used as an emergency locator, a sports whistle, dog training, a safety alarm, etc. At just 4 inches in length, this compact whistle is easy to carry in your pocket or purse. Requires four LR44 batteries (included).
Review by J.M, Cherry Blossom Tours on Feb 10, 2011
I'm a bus driver and tour guide and I use this to announce loading time for the passengers at most sites. Works great and it's always with my bus key.