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In recent decades, wireless doorbell systems that do not require wall wiring have become popular. The doorbell button contains a built-in radio transmitter powered by a battery. When the button is pushed, the transmitter sends a radio signal to the receiver unit, which is plugged into a wall outlet inside the building.
How Doorbells Work. The core of a conventional doorbell is an electromagnet. If you've read How Electromagnets Work, you know that an electromagnet is a coil of wire, often wrapped around a piece of magnetic metal. Electromagnets work on a very simple principle. Running electrical current through wire creates a very small magnetic field around the wire.