Acme Dog Training Clicker

This is the original Acme Dog Training 470 Clicker Cricket WWII-signal. These serious brass versions were issued to WWII Paratroopers who behind enemy lines, needed some type of stealth audio signal to identify each other in the dark. Now used for a specialized method of dog training. 

Originally a child's toy made by the Acme Whistle Company in England but came into its own during WWII when troops used them for signaling each other in the dark of night.