The electric doorbell can be found in many modern homes. The mechanism consists of the bell or gong which gets struck with a spring mounted `clapper'. In addition to these components there is an electromagnet, (most bells have one with two coils inside) and finally a basic, flexible electrical contact called the `bell push' which is mounted remotely usually on the exterior door frame.
When the bell-push is depressed, it allows electricity to flow through the contact and into the electromagnet. This in turn magnetises the clapper's iron arm. The clapper is drawn out on its spring and can then strike the bell as the bell push is released. With the magnetism now gone the spring pulls back the arm to its original position.
In recent years the electronic doorbell has become available, these utilise electronic microchips to generate chimes of bells or melodies. These sounds are then amplified and played through a loudspeaker.
