Most motion detectors take over trivial technical functions. Of course, with rapid advances in technology, complex tasks can be solved. This presentation focuses on typical motion detector applications. Their typical use cases are familiar. For example, automatic doors in a shopping mall, access control, opening barriers, alarm systems, light controls, escalator or vending machine activation, automation of sanitary devices and many more are trigged by motion detection. Most often these applications use PIR-sensors. However, despite its popularity and sophistication, the technology is constrained in some cases. Motion detectors are not perfect and challenges can be caused by their operational environment and the intended target to be detected. For example, motion detection must be functional outdoors and indoors, so weather or light conditions cannot have an impact on their performance. Also, extreme temperatures, moisture, or dust should not cause malfunctions. The sensors must detect various material, clothing fabrics, and differing objects like vehicles or people. For some applications like intrusion alarms, an accurate and correct detection is critical. So, the risk of interference and distraction must be reduced. Sensors must deal with manipulation such as shielding and unwanted triggers generated by small animals.