A reed switch consists of two ferromagnetic nickel-iron wires and specially shaped contact blades (reeds) positioned in a hermetically sealed glass capsule with a gap between them and in a protective atmosphere. The glass capsule is filled with inert gas to prevent activation of the contacts. The ruthenium or rhodium plated contact surfaces are isolated from the outside environment, which protects the contacts from contamination. Reed switches can be operated using a magnetic field generated by either a permanent magnet or current-carrying coil. They induce north (N) and south(S) poles on the reeds. The magnetic attractive force leads to closure of the reed contacts. Upon removal of the magnetic field, contact open again due to the elasticity of the reeds. There are Reed Switches which operate with permanent magnet, while there are Reed Switches operate with coils which can be magnetized by sending current through them. 

Magnets have a natural tendency to attract many things. Though not perceived as a real force, but it does attract human attention when a force acting invisibly draws things to itself. By harnessing this power, humans have made wonderful inventions like the electromagnet and discover lossless conduction phenomenon like superconductivity. Among these many inventions, was the application of magnetism to switch from ON state to OFF and vice-versa in precision devices. One such switching device, which works not by the principles of electricity, but magnetism, is the Reed Switch.