Magnet detection is a safety mechanism that works on the principle of magnetism. The magnet is located in the upper part of the housing and is detected by the camera module when inserted into the housing.
This is important because this is the way the camera module knows it can send you postcards.
When you remove the module from the feeder and take it into the house to charge it in the living room, it will not be able to connect to take pictures.
The magnet detection is also tied to the LED lights - when inserted in the feeder, the LED lights will not light up (unless you click on the button to check the module’s status), in order to not scare the birds away.