A Magnetic Switch has two parts, 1 is the Magnet, 2 is the Reed switch part.
The Reed switch part consists of reed switch and the housing case. The reed switch part is the key part. Some consider the reed switch part the separate product, which will work with circuit coil of device.
How does a magnetic switch work? Simply speaking, the Magnetic switch functions by the reed switch when the magnet part gets close or gets apart. This is 2 ways of usage by getting close and getting apart.
Let's take a fast example of Normally close reed switch here, say set an alarm door magnetic switch on the door, work with security system, once the door opens, the magnet part will get apart from the reed switch, so the moment they get apart, the security system will work and alert someone. This is one of the common usage.
When using the Normally open reed switch, the usage can be more colorful. Again a quick example, set the magnetic switch on door, once the door open, the magnet and the reed switch will get apart, which will cause the magnetic signal and relevant device will be activated.