Motion detector defective

Like other electrical components, motion detectors may also be defective. But repairing is not easy. There are also various sources of error. How to find out if a motion sensor is defective and possibly still repairable, we have summarized for you afterwards.

Technique of the motion detector

To be able to limit a defect in a motion detector, it first has to be determined which type of motion detector is involved. Here are the most common techniques:

  • Infrared motion detector (PIR)
  • Radar or high-frequency motion detector (HF)
  • Photocells Motion

Typical problems of PIR detectors, especially outdoors

In private applications, PIR detectors are especially widespread, ie detectors controlled via infrared. These are usually like all motion detectors made of plastic. Also the special lens (Fresnel lens). This provides a dispersion of the infrared beam, so that the specified range can be covered.

Especially with motion detectors that are used outdoors, this lens is often broken due to the UV radiation. In addition, moisture is added outdoors. This allows the electrical components to corrode quickly. For outdoor use, therefore, only a high-quality motion detector with the appropriate IP rating (dust and moisture proof) should be used.

Alternatively, HF detectors can be used. These have the advantage that they can also be installed concealed - even behind walls, ie in protected interiors or at least under superstructures.

Possible defects in the electrical system

That the built-in motion sensor is broken, is rather rare. Instead, capacitors (Elkos) are also installed in motion detectors. These are often of poor quality as with many other electrical appliances. A defective capacitor is usually to be recognized by the fact that it is inflated.


In addition, other causes of problems with the motion detector may not be excluded. As mentioned earlier, the electrics are affected by corrosion. This also applies to the supply line - depending on how professionally the motion detector was connected, ie also safe against moisture, for example, in a flush-mounted distribution box.

The setting of the motion detector

In addition, some motion detectors can also be adjusted in their sensitivity. Before disassembling the motion detector, you may want to check if you can set the triggering a bit coarser. In addition, low-cost motion detectors can be designed to register transverse movements rather than motion.

If a detector is connected in front of the house in the driveway, it can be in the individual case so that triggering creatures or objects from bottom to top or vice versa reach the trigger area and the detector does not respond.

Protection or overload of the detector

Motion detectors are also designed as a 12 V system. Between the 230 V line and the actual electrical component then a rectifier is connected. If consumers are connected with very high power requirements, this can destroy the circuit of the motion detector without additional protection. Therefore, in such a case, a contactor should be installed in between at the initial installation.

Tips & Tricks

In the house journal you will find numerous guides and instructions on motion detectors. Here, for example, we show you how to connect two motion detectors in series. Of course, we also offer many other topics that you can reach about categories and search.

Video Board: A1 smartwatch, motion sensor defective.