What Is a Motion Sensor? Principles and Technical Features

Motion sensors are core components of security systems that detect the movement of people or objects and output signals to trigger actions such as alarms, video recording, or lighting control.
In security applications, the ability to detect intrusions quickly and accurately is critical. The choice of sensing technology and the design of its installation significantly affect the overall reliability of the system.

■ PIR (Passive Infrared) Sensors
PIR sensors detect infrared radiation (heat) emitted by the human body and determine motion based on changes in the thermal distribution.
In high-temperature environments, the temperature difference between a human and the background may become smaller, potentially reducing detection sensitivity.

■ Microwave Sensors
These sensors detect changes in reflected microwave signals emitted from the sensor, utilizing the Doppler effect.
They are more susceptible to environmental noise such as rain or reflections from metal surfaces. Additionally, the detection area tends to be less clearly defined.

■ Dual Technology
OPTEX’s Dual Technology sensors combine PIR (Passive Infrared) and Microwave (MW) detection methods. The system cross-verifies the detection results from both sensors and only triggers an alarm when both detect motion simultaneously (AND logic).
This approach significantly reduces false alarms.
Dual Technology offers high resistance to environmental factors that often cause false detections in PIR-only systems, such as strong sunlight, vehicle headlights, or sudden temperature changes.

Motion sensors are essential for detecting intrusions in security systems. By detecting the movement of people or objects in real time and integrating with alarm systems and video surveillance, they enable early identification of intruders and immediate response.
Motion sensors contribute significantly to enhanced security, particularly in the following areas:

• Instantly triggers recording, notifications, and deterrent actions by linking with alarms and surveillance cameras the moment motion is detected.
• Enables continuous monitoring without relying on human oversight, even during nighttime or unmanned hours.

• Allows the division of premises into multiple zones, with customizable detection sensitivity and response settings for each area.
• Enables focused monitoring of critical zones (e.g., material storage areas, loading docks), reducing false alarms and improving operational efficiency.

• Works in conjunction with sirens, flashing lights, and voice warnings to immediately deter intruders.
• Simultaneously alerts the surrounding area upon detection, enhancing crime prevention and deterrence.

• In large facilities requiring constant surveillance (e.g., factories, logistics centers, schools), helps optimize the frequency of security patrols.
• Automated detection by sensors reduces labor costs while improving monitoring accuracy.

Outdoor motion sensors are essential devices for achieving “Early Warning” — detecting intrusions before they reach the building.
By installing them in key areas such as property boundaries, approach paths, windows, parking lots, and backyards — the typical starting points of intrusion — they enhance deterrence against crime and enable rapid response through integration with security personnel and video surveillance systems.

OPTEX is a global leader in the field of sensors specialized for outdoor environments, holding approximately 40% of the global market share.
Its stable sensing performance and low false alarm rate are highly regarded, and OPTEX products are used in a wide range of applications around the world — including residential buildings, commercial facilities, infrastructure, and factories.

To fully leverage the performance of motion sensors, it is essential to select the right product and design the system according to the installation environment.
The next article explains how to choose motion sensors based on environmental conditions and specific requirements.