A reed switch consists of two ferromagnetic and specially shaped contact blades (reeds) positioned in a hermetically sealed glass tube with a gap between them and in a protective atmosphere. The plated contact surfaces are isolated from the outside environment, which protects the contacts from contamination. Reed switches are available as form A (normally open) and form C (changeover), and are operated using a magnetic field generated by either a permanent magnet or current-carrying coil. The features that make the reed switch a valuable tool include compact size, low weight, quick response time, long life and low cost. Some common applications are: reed reays, automotive sensors, robotics sensors, security sensors and toys and games. They are also available in moulded packages affording protection from damage and in surface mount styles.
