I’ve never seen any examples of that alarm or the Detexall brand, but the American LaFrance stamp on the inside caught my eye.
American LaFrance manufactured fire engines, rescue vehicles, etc. going all the way back to the steam-powered engines of the late 1870s, before filing for bankruptcy a few years back.
I wonder if this was simply an accessory licenced by the company, or if it was actually produced for and installed in a firefighting vehicle.