How Motion Detection Works

Choose the right tool for the right job.  Are you using the right motion detection technology in your environment?  Often overlooked aspect of motion detection is how it would integrate with the existing security system. And with new security installations motion detection is often understated.


Before deciding on the new security system or upgrades to an existing one, ask yourself which motion detection technology would benefit you and is the best tailored solution for your environment.   The following are the most common motion detection technologies:


PIR Motion Sensors


PIR stands for Passive Infrared.  Those are the most common motion detection sensors that pick up heat signature of objects within the field of view.  To be more specific the sensor detects changes of the amount of infrared radiation within the field of view.  For example the heat signature of human body surfaces in contract to the surrounding environment. The most PIR motion sensors detect infrared wavelengths of 5 µm or longer. The human body emits 10 µm wavelengths.


The amount of clothing or colors a person is wearing make a small difference, but not enough compared to the influence of ambient temperature to avoid detection.  PIR Motion Sensors have a response time of about 0.5 seconds, which represents the interval between the actual movement and the detection of that movement. The duration of the sensor output signal after detection depends on the speed of movement and the magnitude of temperature difference. It usually averages to at least 10mS.  Common PIR Motion Sensors can’t detect motionless objects, they can’t accurately detect direction of movement, and they can’t create thermal images.


Thermal Cameras


A Thermal Camera is not really a camera, because it does not see/detect the visible light.  It simply internally creates a picture composite based on temperature differences between objects in the field of view.  Thermal cameras have an excellent range and they are very efficient in detection through smoke, fog, total darkness, or objects that are camouflaged.  Even though the Thermal Cameras are very effective two drawbacks of them are high price and no ability to recognize the individuals.  For those reasons Thermal Cameras are usually combined with Video Motion Detection Cameras where applicable.


Video Motion Detection Cameras (VMD)


Video Motion Detection Cameras combine the function of a security camera with added software analytics that examine the image as it is being captured.  Video Motion Detection Cameras rely on the quality of the image from the camera and the quality of the analytics software they use.  The downsides of Video Motion Detection Cameras are that they operate in the visible light spectrum, can be blind if there is not enough light, and they can be blinded if there is too much backlighting.  The up site is that they are cost-effective, but could become expensive when trying to cover a very large area.




Radar detection works by transmitting radio waves and receiving the same waves bounced off objects in its field of detection.  Radio waves pass through unsubstantial objects such as rain, falling snow, and smoke. They don’t need the visible light spectrum, and work in total darkness conditions.  Advantages of tracking objects with radar are the ability to detect movement within specific zones, they reducing false alarms; they can detect motion across a wider area and from far away. Radar motion detection is cost effective and well below that of thermal cameras.


There are strengths and weaknesses to all motion detection technologies, and their application should be determined by analyzing the situations in which they would be used and the makeup of components that they are a part of.  Choose the right tool for the right job.  To learn more about motion detection equipment, including radar, infrared, video motion detection cameras, or PIR motion sensors please contact AlarmSavvy by calling 888-999-5589 or email us for more information.  We are here to assist you with your security needs.

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