The gas alarm rattle was a hand operated ratchet device that made a loud clacking sound when turned rapidly. Soldiers of the British Empire forces used rattles in some instances as alarms to warn others of the presence of chemical weapons.
Commonwealth troops used a variety of devices as anti-gas alarms throughout the war. Low maintenance alarms could be improvised by converting empty large-calibre brass cartridge cases into bells or gongs, like dinner bells.
Installing bells, gongs, or air horns in the trenches was a relatively simple matter, but a way to spread the alarm was also required on roadways and temporary positions further to the rear. As a temporary measure, soldiers might bang their bayonets on their steel helmets, but this was not ideal, as it involved removing the helmet and leaving the head exposed.