A fire alarm system has a number of devices working together to detect and warn people through visual and audio appliances when smoke, fire, carbon monoxide or other emergencies are present. ... Alarms can be either motorized bells or wall mountable sounders or horns. A fire alarm system is something that will detect fire and then to warn people of the fire. The detection can be a person seeing the fire, a smoke detector sensing smoke, a building's fire sprinkler system spraying water on a fire.