(n.) An alarm bell, or the ringing of a bell for the purpose of alarm.

Klaxon Mayday SOS air-raid alarm alarm alarm bell alarm clock alarm signal alarum alert all clear beacon blinking light burglar alarm buzzer crostarie fiery cross fire alarm fire bell fire flag five-minute gun flashing light fog bell fog signal foghorn gale warning hooter horn hue and cry hurricane warning lighthouse note of alarm occulting light police whistle sign signal signal of distress siren small-craft warning still alarm storm cone storm flag storm warning two-minute gun upside-down flag whistle