Why does wireless camera system send so many email or APP false alert?

To explain this question, we need know the theory how motion detection works.
The NVR system can detect small image optical change. It can be triggered by small image change from camera. Image is transmitted by light signal.
Therefore, even if there is no object in front of camera such as human, animal or car, system may still be triggered by small light change such as floating cloud, shaking leaf.
Most customers hope the system can only be triggered by big object like people and ignore small movement. But based on the theory how motion detection works, there are false alarm.
It is hard to say the system is faulty since not only ANRAN brand system faces such issue, but also other brands who use light sensor to work for motion detection function.