In 1936, Walter B. Ellwood of Bell Telephone Laboratory invented the magnetic reed switch, and applied for a patent in the United States on June 27th, 1940, with the patent number of 2264746. The basic type is to seal two magnetic reeds in a glass tube. Although the two pieces overlap, there is a small gap in the middle. When the external magnetic field occurs, the two magnetic reeds will contact and then conduct. Once the magnet is pulled away from the switch, the reed switch will return to its original position.
 Structure: Magnetic reed switch consists of two magnetic reeds (usually made of iron and nickel) sealed in a glass tube. The two magnetic reeds overlap with each other but there is a small gap between them. Appropriate external magnetic field will make the two magnetic reeds contact. The contacts on these two reeds are plated with a hard metal layer, usually rhodium and ruthenium, which greatly improves the service life of switching times. Nitrogen or some equivalent inert gas is usually injected into the glass tube, and some magnetic reed switches will make the interior in a vacuum state in order to improve the switching voltage performance.

 Principle: The working principle of magnetic reed switch is very simple. Two magnetizable reeds (usually made of iron and nickel) overlapping at the end points are sealed in a glass tube. The two reeds are stacked with a small gap (only about a few microns) between them. The contacts of these two reeds are plated with a hard layer of metal, usually rhodium and ruthenium, which greatly improves the switching times and product life. The glass tube is filled with high-purity inert gas (such as nitrogen). In order to improve its high-voltage performance, some dry-spring switches will make the interior in a vacuum state. The reed acts as a flux conductor. When not in operation, the two reeds are not in contact; When the magnetic field is generated by the permanent magnet or electromagnetic coil, the applied magnetic field makes the two reeds have different polarities near the end points. When the magnetic force exceeds the elastic force of the reeds themselves, the two reeds will attract and conduct the circuit. When the magnetic field weakens or disappears, the dry reed is released due to its elasticity, and the contact surfaces will separate to open the circuit. The basic structure and components of Form A (normally open) reed switch are switchable. When there is no magnetic field, the reed is in contact with the normally closed piece. When a magnetic field of sufficient intensity is generated, the reed will move to the normally open piece, while both the normally open piece and the normally closed piece are fixed. The two fixed pieces and the swingable reed are ferromagnetic pieces, but the normally closed contact surface of the dry reed is fused and welded to the dry reed by nonmagnetic metal. When placed in a magnetic field, the normally open and normally closed fixed pieces on both sides have the same polarity, and the polarity is opposite to that of the swingable reed. The non-magnetic metal at the normally closed end will isolate the magnetic flux, so when the magnetic force between the normally open end and the swingable reed is large enough, the swinging reed will contact and close with the normally open piece.