Let me add my 2 cents here. Some of the old fire alarm boxes were spring wound like a clock. When the alarm went off, the little wheel would turn. The wheel had cogs in it and the cogs were cut into patterns by the installer. For example the wheel on the flow switch might be 2-4-6 and the wheel on the temperture freeze alarm might be 4-6-8. Then in the central office when an alarm came in the person in charge would look up who's alarm code went off and dispatch the fire dept to the proper location. I know because I had to install some of those wheels.
