Working principle of reed switch

Reed switch is a special magnetic sensitive switch. Its two contacts are made of special materials and encapsulated in a vacuum glass tube. As long as a magnet is close to it, the two nodes of the reed switch will be attracted together to make the circuit conductive. Therefore, it can be used as a sensor for counting, limiting and so on. There is a kind of bicycle kilometer meter, which consists of sticking a magnet on the tire and fixing a reed switch on the side. Installed on the door, it can be used as an alarm and greeting when opening the door. Reed switch will also be used to make "disconnection alarm".