Can be used as a sensor, for counting, limit, and so on. There is a bicycle Code table sensor, which is a magnet on the spokes and a reed tube on the front fork. Installed on the door, can be used as a door alarm, greeting and so on. In the production of "disconnection alarm", dry reed tube is also used.
When the permanent magnet is close to the reed tube, or when a magnetic field is magnetized by the coil around the reed tube, the contact of the reed will induce the polarity opposite. As the polarity of the magnetic poles is attracted to each other, when the magnetic force of attraction exceeds the resistance of the reed, the separated contact will be absorbed; when the magnetic force is reduced to a certain value, the contact is restored to its initial state under the action of the reed Resistance. This completes the function of a switch. So it can be used as a sensor for counting, limiting, and so on. There is a kind of bicycle kilometer meter, that is to stick a magnet on the tyre, at one side fixed two reed tube of dry reed composition. Installed on the door, can be used as a door alarm, greeting and so on. In the production of "disconnection alarm", dry reed tube is also used.