Reed switches are magnetically actuated switches.

Most reed switches are of the Normally Open (NO) type. They close under the influence of a magnetic field. Normally Closed (NC) and toggle (change over) types are also available. They are frequently used in bike computers, detecting the passage of the spoke magnet for calculating the speed, and in laptops to detect whether the lid has been opened or closed.

The body that holds the contacts is mostly made of glass, so be careful when handling them. Inside the glass chamber, a noble gas protects the switch from arcs due to switching. Reed switches are suited to conduct small currents, usually around 100 mA.

Because they can be hidden completely in a prototype without any visible parts, they can give a nice interaction for example when opening something.


  • Maximum voltage.
  • Maximum current.