Noun
An alarm bell, or the ringing of a bell for the purpose of alarm.
Source: Webster's dictionaryThe tocsin you hear today is not an alarm but an alert: it sounds the charge against our enemies. Georges Danton
He is in safety who rings the tocsin. Spanish Proverb
This system was tested nationwide twice in 1961, under codenames Exercise Tocsin and "Tocsin B". Source: Internet