The most important questions and answers about motion detectors

It has probably happened to all of us: You stand in the basement with a full load and desperately try to get the light switch with your elbow. A clear case for the motion detector! Because where the light switches on automatically for us, there is usually a motion detector behind it. These sensors also help us to intelligent lighting and safely illuminate paths in gardens and outdoor areas. But which motion detectors are there and how do they work? What criteria should you consider when buying a motion detector? Find out everything you need to know about this little helper!

  • What is a motion detector?
  • What types of motion detectors are there and how do they work?
  • What is the difference between a motion detector and a presence detector?
  • For which areas of application are motion detectors suitable?
  • What should you look out for when buying a motion detector?
  • How do I set up a motion detector?
  • Does the motion detector require maintenance?
  • Conclusion: courteous electronics with helpful security benefits

Due to the high demand, we have updated this article and added the question “How do I set up a motion detector?”

What is a motion detector?

With the motion detector, the name says it all: it reports movements. More precisely, a motion detector is an electronic sensor. This detects movements in a certain environment and can be used as an electrical switch according to these registered movements.
In our everyday life, we ​​often encounter motion detectors without being aware of them. Because that’s what’s so special about a motion detector: we don’t have to press a switch or take any other action, we just appear and are recognized by the motion detector.
If, for example, the outside light comes on as soon as you approach the house or the doors in the supermarket open automatically, there is usually a motion detector behind it.

What types of motion detectors are there and how do they work?

The generic term of the motion detector summarizes various technologies, all of which are used with the purpose of detecting movement. How it works is very different.
If you want to deduce the technology used from the term “motion detector”, the naming can even be somewhat misleading, depending on the detector. From a technical point of view, the most common type of motion detector does not react to movements, but rather to temperature changes in the environment. In general, all motion detectors infer movement from changes detected in the detection area.
There are basically four types of motion detectors:

  • PIR motion detector
  • HF or radar motion detector
  • Ultrasonic motion detector
  • Camera motion detector

How does an infrared motion detector work?

PIR sensor as a passive eye for moving interiors

The PIR motion detector uses a so-called passive infrared sensor (short: PI sensor), which works with infrared technology and reacts to temperature changes in the covered area.
The sensor, therefore, responds to differences in thermal radiation in its detection area. Basically, it reacts to everything that moves and emits heat – people, cats, cars, aliens, etc. This is referred to as a passive sensor since the PIR detector itself does not emit anything. The moving objects must themselves radiate heat in order to be recognized.
In order for PIR sensors to be able to optimally detect temperature differences, there must be direct contact with the object. They must not be shielded or covered. The sensitivity of the sensors can also be affected by heavy rain or thick winter clothing.

How does an RF motion detector work?

High-frequency or radar motion detectors emit high-frequency electromagnetic waves with small wavelengths. These hit the objects in the covered area and are reflected. The motion detector records the energy reflected by the objects.
Movements in the environment can thus be recognized by changes in the recorded energy. HF sensors can be installed covertly because the electromagnetic waves penetrate materials such as glass or wood. They even work through thin walls or doors.

Note: The difference between PIR detectors and HF detectors is that the latter is independent of heat or thermal radiation and only detect movement. As a rule, even strong temperature fluctuations do not disturb the function of the HF motion detectors. So you can easily blow-dry yourself in the mirror image of the sensor.

How does an ultrasonic motion detector work?

Like HF motion detectors, ultrasonic motion detectors are active sensors. Ultrasonic motion detectors, unlike RF detectors, emit sound waves instead of electromagnetic waves to detect changes in the surveillance area.
Since sound waves travel through the air, ultrasonic motion detectors cannot be installed near strong sound waves, behind curtains, above heat sources such as radiators, and in the area of ​​air vents.

How does a camera motion detector work?

Camera sensors are also used in motion detectors. Movements are detected by electronic evaluation of image data. So if the image recorded by the camera changes, the camera sensor registers this change as a movement by comparing it with previously recorded image material.

What is the difference between a motion detector and a presence detector?

Presence detectors are particularly sensitive motion detectors
Presence detectors

A presence detector is a sensor that detects the presence of people in a room, even during quiet activities. The key difference between a presence detector and a motion detector is the sensitivity of the sensors. Furthermore, presence detectors measure constantly, while motion detectors only react to the first movement.
For example, if you control a light switch using a motion detector in the basement, it will turn on the light as soon as you enter the basement. After a certain time, the light switches off again automatically and if you weren’t fast enough, it’s time to dance in the dark in front of the motion detector.
A light switch controlled by a presence detector, on the other hand, also switches on the light when you enter the basement and constantly checks whether you are still in the room. It then switches the light off automatically as soon as you are no longer in the room. Without dancing.
Occupancy detectors are mainly installed in living and working areas, while motion detectors are better suited for outdoor security devices or as light switches in hallways and stairwells.

Which sensors does a presence detector use?

Particularly high-quality sensors are used so that presence detectors do not miss even the smallest movement. Both HF sensors and PIR sensors are installed for this. For lighting purposes, HF sensors are usually combined with a twilight switch so that the light is only switched on when it is dark.
Ultrasonic sensors are often used in offices because their high sensitivity also registers optimally seated activities without the people in the room having to wear an antenna on their heads.

For which areas of application are motion detectors suitable?

The areas of application of motion detectors are very diverse and vary depending on how they work.

  • Typical areas of application include:
  • light switch
  • presence detector
  • intruder alarm systems
  • video surveillance
  • traffic signals

Which motion detector is a light switch?

PIR detectors are the most common motion detectors and are used both indoors and outdoors. They are used particularly frequently as light switches outdoors, in stairwells, corridors and garages. On the other hand, ultrasonic sensors for light switches are particularly suitable for long corridors and hallways.
HF sensors are particularly sensitive and are therefore mainly installed indoors. Because while a reaction of the motion detector with every leaf blowing past in the garden is rather undesirable, it is precisely this sensitivity in the building that offers certain advantages. High-quality high-frequency sensors, for example, already detect when the door handle is pressed and can thus switch on the light before you are completely in the room.
Since they can be installed in a concealed manner, they can also be installed in lights out of sight for the consumer and therefore do not have to fit into the decorative concept. And since RF sensors can not only go through walls but also leave them cold to heat and sudden changes in temperature, they are also used in storefront doors. HF switches open the doors even to hot-headed customers undeterred.

The popular sensitive little thing: iHF sensor for outdoor use
sensor for outdoor use

What is an iHF sensor?

The abbreviation “iHF” stands for intelligent HF sensors, sometimes also called smart HF sensors. While conventional HF sensors are not suitable for outdoor use due to their sensitivity, the technology in iHF motion detectors has been further developed so that the sensors can distinguish human movements from rain, leaves or jumping insects. With this new intelligence, iHF sensors are very popular with outdoor motion detectors.

Tip: Would you like your outside light to switch on automatically when it is dark and not only when people are nearby? The easiest way to do this is with so-called twilight sensors.

Which motion detector for alarm systems?

In burglar alarm systems, combinations of different motion detectors are usually used to reduce the risk of false alarms. For example, there are so-called duo PIR detectors, which are made up of two separate PIR sensors and only trigger an alarm when both sensors react. The principle is similar for dual detectors: A PIR sensor is combined with an HF sensor or an ultrasonic sensor and the alarm is only triggered when both detectors react.
For intruder alarm systems with high-security requirements, detectors with anti-masking can also be used. These detect when the sensor is taped or sprayed, for example, and report the cover to the alarm system via a separate output.

Which motion detector for video surveillance?

Motion detectors with camera sensors are often used in video surveillance. If the sensors register a change in the image recording, the recording of the video surveillance system can be switched on. The recording capacity of the monitoring system is thus used more effectively and the search for possible incidents is also easier.
Depending on the surveillance system, when the sensor is triggered, not only the video surveillance but also the light can be switched on via a signal and the alarm can be triggered accordingly.

Note: PIR sensors are also used as traffic cops. Based on the heat emitted by the vehicle engines, they monitor the traffic volume on motorways and at traffic lights in order to control them optimally. Traffic jam warnings and recommended speeds are also determined in this way.

What should you look out for when buying a motion detector?

From the alarm system to the basement light – there are numerous different motion detectors and applications, but some basic criteria should always be considered when choosing the right motion detector.
These purchase criteria are to be observed for the motion detector :

  • detection range and detection angle
  • Range
  • installation area
  • IP protection class
  • mounting type
  • mounting options
  • Setting options (e.g. light duration)

Detection area, detection angle & range

If a sensor is to work reliably, the question arises as to which area it should monitor. Basically, the larger the detection angle, the larger the detection range of the sensor. Motion detectors are available with a detection angle between 90 and 360 degrees. The latter is particularly recommended for motion detectors for ceiling mounting.
Since the requirements vary depending on the structural situation, the angle on the sensor can be adjusted as needed with some detectors. Also, make sure to distinguish between the horizontal and vertical detection areas and check whether the range of the sensor is sufficient. A long-range is often crucial, especially for outdoor applications.

Tip: If in doubt, opt for a motion detector with a large detection angle and adjust the detection area later using screens if necessary.

Installation area & IP protection class

It not only has to be clarified whether the motion detector should be installed indoors or outdoors, but also the necessary connection options should ideally be located in the vicinity of the motion detector.
If the motion detector is installed outdoors, it must be weatherproof. Therefore, a motion detector for outdoor use must have at least IP protection class 44. For indoor applications, IP protection class 20 is usually sufficient.

Tip: When outdoors, make sure that the detection area of ​​the motion detector is not affected by regrowing plants or reflective surfaces over a longer period of time.

Type of mounting & mounting options

The type of mounting also varies depending on the installation area. Motion detectors can be attached to the wall or ceiling, for example, although ceiling mounting is recommended for an ideal detection area for indoor applications. Some models are also designed to be installed in outside corners.
Outdoors, we recommend mounting the motion detector at a height of 2 meters or more. This means that it cannot be easily manipulated by unauthorized persons and the higher it is installed, the larger the area covered.

This motion detector with creep-under protection also keeps an eye on crawling intruders
motion detector

Setting Options

Not only the detection angle of the sensor can be adjusted with some models, but also the lighting duration and the light sensitivity. While the adjustable light duration ranges from a few seconds to several minutes, the light sensitivity can usually be regulated up to 2000 lux.
Also pay attention to additional functions that are helpful for your specific application, such as e.g. B. an integrated twilight switch or creep protection. The latter is realized by a special lens or a second sensor and prevents the detection area from being bypassed.
Note: If the motion detector is coupled to a light source, it should be a light source that emits full luminous flux directly. In addition, the maximum electrical output in watts permitted for the detector must not be exceeded by the light source.

How do I set up a motion detector?

In order for a motion detector to do its job as desired, it must also be set correctly after installation.
The following factors, in particular, must be taken into account:
Position: Depending on how they work, the sensors can be affected by waste heat from heating and air conditioning systems, direct sunlight or moving objects such as flags or trees. Check the environment for possible sources of error.
Height: The height is crucial for the correct setup of the motion detector. A height of 2.50 m is ideal for a light switch on most surfaces. Not only the orientation of the motion detector but above all that of the lens is crucial here. It should have a good “view” of the area to be monitored.
Twilight switch: The brightness threshold can be used to set when the motion detector switches on the light. Experiment with different settings to ultimately determine the optimal brightness value for you.
Timer: The timer can be used to specify the periods at which the motion detector should be operated. Setting options vary by model.
Switching duration: With some motion detectors, you can set how long they remain in operation. For example, it can be specified that the outdoor light is on for 60 seconds after a movement.

Note: Be careful not to set the brightness threshold too high. Because if there are street lamps in the vicinity, these with a brightness of mostly 15 lux can mean that the threshold is never reached and the motion detector does not switch.

Does the motion detector require maintenance?

Dirty glasses make it difficult to see, and so does the sensor of the motion detector. Proper cleaning of the motion detector is, therefore, an important care aspect and at the same time prevents long-term damage.
The sensor as the “eye” of the motion detector should always be cleaned of dust and other dirt so that it can function properly. Cleaning can be done quickly with a damp cloth. For stubborn dirt, you can also carefully spread a mild scouring agent on the detector with the cloth and wipe it off after a short exposure time.
If the motion detector gets dirty very often, installing it in a different location may help. Ideally, the motion detector should be protected as well as possible from wind and weather as well as direct sunlight.

Simple tips for maintaining a motion detector

While the motion detector reliably reports movements, it does not provide any information about possible damage. However, with a few maintenance steps, you can quickly track down common problems.


Is it still dawning on your switch?

Check cables: While the supply lines in indoor applications usually only have to deal with dust, outdoors they are exposed to wind and weather and should always be cleaned and thoroughly examined. Broken or bare cables can not only lead to malfunctions but are also dangerous.
Check the battery: If your motion detector is a battery-powered solution, you should check the batteries regularly and replace them if necessary.
Check the battery: In the case of solar-powered solutions, the batteries should be checked regularly and replaced if they can no longer absorb sufficient energy.
Defective light bulb: You wave wildly and the light still doesn’t come on? Maybe it’s not the motion detector, but the light bulb. Check them and replace them if necessary.
Check the twilight switch: If your motion detector switches the light on at the wrong times, the twilight switch may need to be reset.

Conclusion: courteous electronics with helpful security benefits

Motion detectors are becoming increasingly popular and are being developed with increasing precision. They are available as light switches outdoors or in stairwells, as presence detectors in offices, as traffic assistants in traffic lights and in many other areas of application. A distinction is made between motion detectors according to the types of detection by infrared, high-frequency waves, ultrasonic waves or cameras.
Apart from the different technologies used in the motion detector, motion detectors also differ in terms of other criteria such as the detection area, the range and the available setting options. The installation area and mounting method should also be determined before purchase.
Once the motion detector is successfully in operation, it should be checked regularly. While it is easy to spot when the motion detector is not working properly with light switches, lack of maintenance can lead to security problems, especially with alarm systems. Whether indoors or outdoors – every motion detector is happy about a little care every now and then and then reacts particularly attentively again.