A circuit that completes itself
What Happens When You Press a Doorbell?
The button is not a bell. It is a gap in a circuit that your finger closes for a moment.
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Step 1 of 5
Electricity needs an unbroken loop.
Current only flows if there is a complete path from one end of the supply back to the other. A doorbell button is a deliberate break in that path.
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Step 2 of 5
The current makes a magnet.
Wire wound into a coil becomes a magnet whenever current runs through it, and stops being one the instant the current does.
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Step 3 of 5
The magnet moves a hammer.
That pull yanks a small iron arm across and strikes a metal bar or dome. Let go of the button and a spring pulls the hammer straight back.
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Step 4 of 5
An old bell buzzes by breaking itself.
In a trembler bell the hammer's own movement opens a second contact, killing the magnet, so the spring pulls it back — which closes the contact again. It rattles.
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Step 5 of 5
A modern chime just plays a recording.
Two-note chimes strike two tuned bars. Wireless ones do not even run a wire to the door: the button sends a short radio message to a speaker indoors.
Wired doorbells run on about 8 to 12 volts from a small transformer, which is why the button can be a bare pair of contacts outdoors in the rain.
The short version
Pressing a doorbell closes a gap in a circuit, current turns a coil into a magnet, and the magnet swings a hammer at something that rings.
Try it yourself
Hold the button down on an old trembler bell. It buzzes continuously because it is breaking and remaking its own circuit dozens of times a second.
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