An electrical circuit is closed and complete when the button is pressed. Electrical current instantly rolls onto a transformer that immediately reduces the household 120-240 AC voltage to just 10-20 volts. This 10-20 volt current then goes off into the electromagnet of the signal mechanism.
A doorbells circuit is found inside the signaling mechanism. This is actually a secondary circuit, a type of self-interrupting circuit, looped around the electromagnet. The inbound 10-20 volt current coming from the transformer sets the electromagnet into motion. This results into an electromagnetic field. Once actively magnetic, it attracts a flexible metal contact arm. In an off situation, when the button is not being pressed and where there is no magnetic field and no current, this contact arm stays in its place atop a static contact. As the contact arm is lifted and magnetically drawn to the electromagnet, it breaks open the secondary circuit, halting the flow of electric current in that circuit and de-energizing the electromagnet. The electromagnet, in turn, loses energy and releases the contact arm. The arm returns to the contact seat. The resulting sound is actually the contact arm striking the magnet and the contact in succession. This action happens very rapidly. When the button is pressed long enough, the occurrence will repeat itself. Hearing-impaired individuals use a visual signal format that uses light bulbs.
