Reed switch facts for kids

A reed switch, which uses a magnet to turn on and off.

A reed switch is a special kind of switch that uses magnetism to work. Think of it like a tiny gate that opens or closes when a magnet comes close. When you bring a magnet near, the switch turns on. When you move the magnet away, it turns off again.

If the magnet is an electromagnet (a magnet made with electricity), the reed switch becomes a "reed relay". A smart inventor named W. B. Ellwood created the reed switch in 1936 at Bell Telephone Laboratories.

How Does a Reed Switch Work?

A reed switch has two small pieces of metal inside a sealed glass tube. These metal pieces are called "reeds." They are usually made of a special magnetic material.

Normally, the reeds are slightly apart. This means the switch is "off" and electricity cannot flow through.

Turning the Switch On

When a magnet comes close to the glass tube, the reeds become magnetized. They act like tiny magnets themselves. Because opposite poles attract, the two reeds pull towards each other. They touch, closing the circuit and turning the switch "on." Now, electricity can flow.

Turning the Switch Off

When you move the magnet away, the reeds lose their magnetism. They spring back to their original position, separating from each other. This opens the circuit, turning the switch "off."

Where Are Reed Switches Used?

Reed switches are very useful because they are sealed. This protects them from dust, dirt, and moisture. They are also very fast and reliable.

You can find reed switches in many everyday items:

• Door and window alarms: A magnet is on the door, and the reed switch is on the frame. When the door opens, the magnet moves away, and the alarm sounds.
• Laptops: Some laptops use reed switches to detect when the lid is closed.
• Bicycles: They can be used in bicycle speedometers to count wheel rotations.
• Washing machines: To detect if the lid is closed before starting.
• Security systems: For sensing movement or entry.

Images for kids

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  (from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters.

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  Reed switch, contact detail.

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  Reed switch diagrams from Walater B. Ellwood's 1941 patent, Electromagnetic switch. It illustrates a single pole, double-throw (SPDT) device. Descriptions from the patent text are as follows: Fig. 1 - device shown in nonoperated position Fig. 2 - device shown in operated position Fig. 3 - cross-section 1 - glass envelope 2 - terminal 3 - resilient magnetic member 4 - non-magnetic member 5 - conducting member 6 - magnetic member 7 - insulating piece

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  A reed relay from a TXE-3 telephone exchange

See also

In Spanish: Reed switch para niños