Abstract: An alarm bell especially adapted to be used in combination with a system which simultaneously detects smoke, fire, current failure, and unauthorized entry into an enclosure. The alarm bell has a housing which suports a bell dome. A mechanical motor is contained within the housing and is connected to actuate a first clapper which strikes the dome and sounds an alarm. A second clapper is actuated by an electric motor and is also placed adjacent to the dome. The first clapper cooperates with an electro-magnet such that the magnetic attraction therebetween prevents movement of the first clapper when the electro-magnet is energized. Accordingly, the electro-magnet can be connected to the same source of current which is used to energize the second clapper so that should the source of current fail, the electromagnet will release the first clapper thereby causing the mechanical motor to sound the alarm.