This was first introduced during WW1 on the Western Front, and the results were devastating. Soon everyone was issued a gas mask and was required to carry one with them at all times. Various types of "gas alarms", from simple wooden rattles to mechanical sirens were employed to help warn the soldiers that it was time to put the mask on. This is a great example of a U.
WW1 KLAXON brand gas alarm, which produces a very loud noise when hand cranked. Plaque on Horn Reads as follows.(SERIAL NUMBER ON LOWER LEFT CORNER) G 4162.