Reed switch

The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by W. B. Ellwood. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. There are two types of reed switches: "normally open" reed switches and "normally closed" reed switches. The metal reeds on a normally open switch stay open when there is no magnet near the switch. In the presence of a magnetic field, the contacts of a normally-open reed switch will close. A normally-closed reed switch is closed when it is not near a magnet; as a magnet is brought close to it, a normally-closed switch will open.The switch may be actuated by a coil, making a reed relay[1], or by bringing a magnet near to the switch. Once the magnet is pulled away from the switch, the reed switch will go back to its original position.Reed switches are used in reed relays, which are used for temporarily storing information in mid-20th Century telephone exchanges. As well, they are for electrical circuit control, particularly in the communications field; as proximity switches for burglar alarms and as switches in electronic pedal keyboards used by pipe organ players and in electronic children's toys which have sound effects that need to be activated.