Before 1831, doorbells were messy and non-electric. They worked by twisting a key-like mechanism that struck a bell on the other side of the door or by pulling a rope that rang a bell inside the house. They were most popular in large estates and houses that needed a bell that was loud enough to sound through the entire house to announce the arrival of a visitor. In fact, similar mechanisms using bells are still used today in retail stores to announce a customer. In 1831, doorbells changed. Instead of a bunch of ropes and hardware connecting the outside of the house to the inside of the house, simpler doorbells using electricity were invented by Joseph Henry.
Electric doorbells work by producing a sound when an electric current is applied to a circuit. These doorbells consist of one or more electromagnets which are made of coils of wire wrapped around around a small piece of metal. When electricity passes through the coils of wires, a magnetic field is created. This field pulls the armature toward it causing a clapper to strike the bell. When you press the doorbell from the outside, the circuit is complete and electricity flows to the electromagnet or electromagnets. However, the electricity from the house is 120v but the doorbell needs a lower voltage so the doorbell has a transformer in it which converts the voltage.
There are two major types of electric doorbells.
The first, a simple ding-dong doorbell, use the magnetic field created by the electromagnet to move a magnetic piston to strike two tone bars:
The second, a buzzer doorbell, uses a contact arm to interrupt the circuit and make the electromagnet stop. The contact arm falls back into position which starts the circuit again. The sound of the contact arm hitting the electromagnetic creates the buzzing noise you hear.
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