Electric Bells and Buzzers
From DT Online
Electric bells are electromagnetic devices with contacts arranged so that once the coil is energized the armature is attracted to it and the circuit is broken.
Once broken the coil is de-energized and the armature springs back to complete the circuit once more.
Each time the armature is attracted to the coil the hammer strikes the bell. This continues in an oscillatory manner until the power is switched off.
Bells normally work on low voltage typically 6 volts. Bells are used as outputs for alarm circuits.
Buzzers are usually of the single tone variety and are normally rated between 6 and 24 volts.
They are suitable for alarm circuits, test equipment, timing and control.
To achieve maximum sound ouput from the device it should be firmly mounted.