A fire alarm is an electronic sounder or a bell. The alarm makes a loud, high pitched sound to notify people that there is a fire in the building. The sounders can be programmed to sound different tones. Most fire alarm sounders in Europe sound like a siren.

A fire alarm system is a building system designed to detect, alert occupants, and alert emergency forces of the presence of fire, smoke, carbon monoxide, or other fire-related emergencies. Fire alarm systems are required in most commercial buildings. Wikipedia