the.com/fire alarm

means A warning device (or a false-alarm-prone event) designed to detect fire or smoke and alert people to evacuate before things get worse.

from A straightforward compound: 'fire,' from Old English fyr, and 'alarm,' which traces back through French alarme to the Italian battle cry all'arme — 'to arms!' — the cry soldiers shouted when danger approached. Mechanical fire alarm systems emerged in the 1800s alongside electric telegraphy, letting cities and buildings wire up networks to summon help the instant smoke was spotted. So the word still carries its old military urgency — 'to arms!' — just redirected from invading armies to overcooked toast.