Acrn is a whistle that has to be held in a particular way with both hands in order for the right airflow creating cavity to exist. If used properly this whistle can create very high volume sounds. As a keychain it could be a good outdoor/hiking safety whistle that will last for a hundred years if made out of metal. It was inspired by a trick my parents taught me as a kid, which was a way you could use acorn caps as a whistle. I wondered why nobody had turned it into a product. I currently have several functional prototypes.