In February 1938, a new invention was introduced to stop fire alarm pranksters. If a person went to “sound the alarm” they would have to insert their arm into a special compartment to activate the signal dial. Immediately after activating the alarm, the person’s arm was locked in the compartment until police or firemen arrived with a key. It was a good idea to catch pranksters, however, for obvious reasons, a bit flawed if there was an actual fire….
After a bit more research, it sounds like these fire boxes would sit outside of buildings, a more logical location than the alternative. Also the photo looks as if the trapping compartment came off the box so a person could walk away after initiating the signal wearing a rather bulking bracelet. Regardless of where it would be located or the specific mechanics, the firebox was not the best invention the world had ever seen nor was it the worst!