A tocsin is an alarm bell — and more exactly, the ringing itself, rung to warn a whole town that something terrible is happening: fire, enemy soldiers at the gates, flood. Before radio and phones, the church or town-hall bell was how everyone found out at once, and the way it was rung told people this was danger, not a normal service. The word covers both the bell and the sound. It belongs to history and to literature; nobody says it about a modern fire alarm. Writers still reach for it as a figure of speech — 'a tocsin of war', 'the report sounded a tocsin' — meaning a loud public warning that something bad is coming. When you meet it, you are almost certainly reading an old novel, a history book, or a deliberately dramatic piece of writing.

警鐘、警鐘聲（古時候用來示警的鐘；現在多用於文學或比喻）