In the field of security alarms, each technological iteration reshapes the boundaries of security. From traditional iron fences and burglar bars to today's electronic fences, and now to intelligent, contactless detection, burglar alarm technology is rapidly developing towards precision, reliability, and intelligence.

In this technological revolution in the security industry, millimeter-wave radar and infrared sensors, as two mainstream detection technologies, are engaged in a fierce competition regarding sensing capabilities, environmental adaptability, and future forms. This article briefly explains the advantages, disadvantages, and differences between the two.

Principle Differences—Different "Senses" of the Physical World

The most fundamental difference between millimeter-wave and infrared technologies stems from their different physical dimensions of perception.

Infrared Sensing: A Passive "Temperature Difference Eye" Relying on Thermal Radiation

Infrared sensing technology is mainly divided into active detection and passive detection.

Passive infrared (PIR) detection technology is the most common type in the security field. Its core principle lies in detecting changes in infrared thermal radiation at specific wavelengths. The human body, as a constant-temperature source, emits infrared radiation with a wavelength of approximately 10 micrometers, creating a temperature difference with the environmental background. When a human body enters the infrared detection area, its thermal radiation is focused by a Fresnel lens onto a pyroelectric sensor, causing a change in charge and generating an alarm signal. This is a passive sensing method that does not require emitting infrared signals; it only needs to capture changes in ambient heat in real time to trigger an alarm.

Active infrared detection technology is completely different from passive infrared. It consists of two parts: a transmitter and a receiver (such as an infrared beam detector), forming multiple invisible beam "fences" between them. When the beams are blocked (such as when someone crosses the beam), the receiver does not receive the transmitted signal, thus triggering an alarm.

Millimeter-wave radar: "Detection waves" of active transmission and analysis

Millimeter-wave radar typically operates in the 10GHz to 100GHz frequency band (wavelength approximately 1-10 millimeters) and is a type of active detection technology. The principle behind millimeter-wave radar detection lies in its continuous transmission of high-frequency electromagnetic waves into space and reception of the echoes reflected back from targets. It calculates distance, frequency shift, and phase change by using the time difference between the transmitted and received signals. Because of this principle, millimeter-wave radar can accurately determine the distance, speed, angle, and even minute movement information of targets within its field of view, enabling the detection of moving objects. This principle also means that millimeter waves are no longer limited by temperature and can only detect moving objects.

Performance Showdown – A Comprehensive Comparison of Advantages and Limitations

Based on their working principles, these two technologies exhibit completely different performance characteristics in reality. The following table provides a core comparison between the two.

Comparison Dimensions

millimeter-wave radar

Infrared

Detection Principle

It actively emits electromagnetic waves and analyzes the distance, speed, angle, and micro-motion of the object under test based on the echo.

Passive infrared (PIR): Detects changes in infrared thermal radiation.

Active infrared: Detects objects that block the infrared beam.

Environmental adaptability

Extremely strong. It can penetrate thin fabrics, smoke, and dust, and is virtually unaffected by sunlight, temperature, rain, snow, fog, or other adverse weather conditions, allowing it to work around the clock.

Relatively weak. Passive infrared is susceptible to interference from sudden changes in ambient temperature, hot air currents, and strong light sources.

Active infrared performance deteriorates in fog, rain, snow, and dust storms, and is highly susceptible to false alarms caused by obstructions from fallen leaves, birds, etc.

Detection capability and accuracy

High-precision multi-dimensional sensing. It can measure distance, speed, and location, distinguish between stationary and minute movements, and identify motion trajectories.

Relatively limited. Passive infrared only detects movement over a wide area.

Active infrared only detects beam obstruction and cannot distinguish the properties of the obstructing object.

Anti-interference and false alarm rate

Low false alarm rate.

The algorithm can filter out noise from things like swaying curtains and pet activity, accurately identifying human characteristics.

The false alarm rate is relatively high.

Passive infrared is sensitive to small animals and temperature changes; active infrared has no ability to distinguish non-invasive obstructions.

Installation and Complexity

The requirements are high.

The beam coverage angle needs to be considered, and installation directly opposite large metal structures should be avoided.

Relatively simple.

Passive infrared sensors need to avoid being directly facing heat sources and have obstructions in their detection path.

Active infrared sensors require precise focusing and must ensure there are no obstructions between the transmitter and receiver.

cost

Chips and signal processing systems are complex and currently expensive, but their costs are rapidly decreasing with technological advancements.

Low cost. Mature technology, complete industrial chain, and low operating costs.

Scene Differentiation – Location-Specific Security Strategies

The advantages and disadvantages of detection technologies directly lead to the differentiation of application scenarios.

Infrared technology, with its cost-effectiveness and simple reliability, dominates the basic security market where high precision requirements are not necessary. Passive infrared is used for intrusion detection on doors, windows, and balconies in homes, while active infrared is used for perimeter security in residential communities.

Millimeter-wave radar, with its superior accuracy and environmental robustness, is becoming the preferred choice for high-end, complex, and intelligent security needs. Applications include airports, oil depots, nuclear power plants, prisons, and other locations with stringent requirements for false alarm rates and reliability. In smart homes, millimeter-wave radar can achieve true presence detection, turning lights on when someone enters and off when they leave, and can distinguish whether a user is stationary or has already left, thus precisely controlling equipment such as air conditioning and lighting to achieve energy saving and comfort.

Future Convergence – From Single Technology to Intelligent Sensing Networks

From a development perspective, millimeter-wave and infrared are not simply replacements, but rather moving towards convergence and symbiosis. The limitations of single-technology detectors are being overcome by the concept of "multi-technology detectors," such as combining infrared and microwave detectors, which only trigger an alarm when both are activated simultaneously, greatly reducing the false alarm rate.