User Quote: “People say mmWave is more reliable than PIR, but I get false triggers sometimes. Am I missing something?” — Source: Reddit r/homeassistant
Introduction
Smart homes and intelligent buildings rely heavily on presence detection. Without it, lights may turn off when you’re still in the room, or air conditioning may waste energy when nobody is there. For decades, PIR (Passive Infrared) sensors have been the default choice. More recently, mmWave radar sensors have entered the market, promising greater accuracy and richer features.
But as real-world users have noticed, the situation isn’t always so simple. One Reddit comment highlights the frustration: while mmWave is said to be “more reliable,” it can still create false triggers. This raises an important question — is mmWave truly more reliable than PIR, or does the answer depend on context and setup?
How PIR Sensors Work
To understand the comparison, we need to look at the fundamentals. PIR sensors detect motion by capturing changes in infrared radiation — essentially, heat differences. When a person moves across the sensor’s field of view, the sudden change in heat triggers an event.
This mechanism makes PIR highly effective for basic motion sensing. It’s inexpensive, energy-efficient, and widely used in lighting systems, alarms, and other simple automation tasks. In fact, the U.S. Department of Energy recognizes PIR-based occupancy controls as a proven tool for energy savings in commercial buildings.
However, the simplicity of PIR is also its biggest drawback. If someone sits still for too long, the sensor may assume the room is empty. This limitation becomes frustrating in modern smart homes, where users expect continuous and seamless presence detection.
How mmWave Sensors Work
mmWave radar takes a different approach. Instead of measuring heat, it emits electromagnetic waves in the 24–77 GHz band and analyzes the reflections. This allows the sensor to detect not only large movements but also tiny micro-motions like breathing or subtle hand gestures.
This ability makes mmWave much more versatile than PIR. It can confirm that a person is present even if they’re perfectly still. It also offers wider and more flexible coverage, and is less affected by environmental factors such as sunlight or HVAC airflow.
That said, mmWave is not without challenges. Because it is highly sensitive, incorrect installation can cause false alarms. For example, reflections from walls or interference from moving curtains may confuse the sensor. This explains why some users on Reddit report unexpected behavior, despite mmWave’s technical superiority.
Strengths and Weaknesses in Real-World Scenarios
When we place PIR and mmWave side by side, the differences become clearer.
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Static detection: PIR fails if a person sits still, while mmWave can detect breathing or posture changes.
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Pets: PIR often ignores small pets, which is sometimes good. mmWave may detect them unless thresholds are properly set.
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Coverage: PIR has limited, fixed coverage. mmWave provides broader, adjustable zones but requires careful placement to avoid reflections.
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Environmental sensitivity: PIR can be disrupted by heat sources. mmWave resists thermal interference but reacts to objects in motion.
In short, PIR is simple and reliable for basic “motion = presence” use cases, while mmWave supports more complex and human-centered scenarios, such as smart offices or healthcare monitoring.
Optimizing Reliability
If mmWave is so advanced, why do false triggers still happen? The answer usually lies in setup, not in the sensor itself. Reliability depends on a combination of placement, configuration, and integration.
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Placement: PIR should avoid direct sunlight or HVAC vents. mmWave should not point toward windows, fans, or thin partitions that can reflect signals. Mounting on ceilings often gives the best coverage.
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Sensitivity and thresholds: Many mmWave modules, including Linpowave presence detection radars, allow fine-tuning of sensitivity. Lower settings reduce false alarms from pets or background movement. PIR sensors may offer adjustable delay timers to avoid rapid toggling.
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Sensor fusion: In many commercial systems, PIR and mmWave are combined. PIR acts as a reliable motion trigger, while mmWave ensures continuous detection. The Ministry of Industry and Information Technology of China has highlighted such sensor fusion as a trend in smart building standards.
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Ongoing testing: Just like smoke detectors, presence sensors benefit from routine checks. Firmware updates for mmWave modules may also improve performance over time.
Conclusion
So, which is more reliable: PIR or mmWave? The answer depends on your needs.
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If you want an inexpensive, low-power way to trigger lights when someone enters a room, PIR is enough.
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If you need accurate, continuous presence detection — for example, to keep HVAC running when someone is quietly working — mmWave is the better choice.
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For maximum reliability, combining both offers the best balance of cost, accuracy, and resilience.
Ultimately, mmWave does live up to its reputation for advanced presence detection, but only when installed and configured correctly. In many cases, it’s not the sensor that fails, but the way it’s used.
👉 To learn more about practical mmWave applications, visit Linpowave’s mmWave sensor solutions, where radar modules are designed for smart homes, offices, and industrial environments.
FAQ
Q1: Why does my mmWave sensor trigger when no one is present?
Likely due to high sensitivity or reflections. Try adjusting thresholds or changing placement.
Q2: Can PIR and mmWave work together?
Yes. Fusion of PIR and mmWave ensures fewer false negatives and false positives.
Q3: Do mmWave sensors work through walls?
Partially. They can sense through materials like drywall, but accuracy decreases and false triggers may increase.
Q4: Which is more energy efficient?
PIR is extremely energy-efficient. mmWave consumes more power but delivers richer features.
Q5: Which should I choose for my smart home?
PIR for simple motion-triggered lighting. mmWave for reliable continuous presence. Fusion for best performance.