Detecting motion and presence is a key function in security systems, lighting control, automation and smart home applications. The most common technologies used for this purpose are PIR (Passive Infrared) sensors and microwave radar sensors.
This article explains how these sensors work, their differences and when to use each type.
PIR Sensors: Passive Infrared Detection
- Detect changes in infrared radiation (heat)
- Common module: AM312
- Output: digital (HIGH/LOW)
PIR sensors do not emit any signal. They detect motion by sensing changes in heat patterns, typically caused by humans or animals moving in the field of view.
Advantages:
- Very low power consumption
- Simple digital output
- Reliable for detecting people
Limitations:
- Cannot detect stationary objects
- Sensitive to temperature changes
- Limited detection angle and range
Radar Sensors: Microwave Motion Detection
- Use microwave signals to detect movement
- Common modules: RCWL-0516
- Output: digital or analog
Radar sensors actively emit microwave signals and detect motion based on changes in the reflected signal (Doppler effect).
Advantages:
- Can detect motion through materials (plastic, glass, thin walls)
- More sensitive than PIR
- Not affected by temperature changes
Limitations:
- Higher power consumption
- More prone to false triggers
- Less selective (detects any movement, not just humans)
PIR vs Radar Comparison
| Feature | PIR Sensor | Radar Sensor |
|---|---|---|
| Detection Type | Heat (infrared) | Microwave reflection |
| Detects Humans | Yes (optimized) | Not selective |
| Detects Through Walls | No | Yes (limited) |
| Power Consumption | Very low | Moderate |
| False Triggers | Low | Higher |
Detection Range and Coverage
- PIR sensors typically cover 5-7 meters
- Radar sensors can detect motion over a wider area
- PIR sensors use Fresnel lenses to shape detection zones
Proper placement is critical for reliable operation.
Adjustable Parameters
Many PIR modules include adjustable settings:
- Sensitivity (range)
- Trigger time (output duration)
- Trigger mode (repeatable / non-repeatable)
Radar modules often have fewer adjustment options but may allow sensitivity tuning.
Common Mistakes
- Mounting PIR sensors near heat sources (radiators, sunlight)
- Expecting PIR sensors to detect stationary people
- Using radar sensors in environments with moving objects (fans, curtains)
Practical Recommendations
- Use PIR sensors for lighting control and human detection
- Use radar sensors when detection through materials is required
- Combine both for improved reliability in critical applications
Power and Integration
- PIR sensors typically operate at 5V
- Radar sensors often operate at 3.3V to 5V
- Output is usually a simple digital signal
Conclusion
PIR and radar sensors provide two different approaches to motion detection. PIR sensors are efficient and reliable for detecting people, while radar sensors offer higher sensitivity and the ability to detect movement through obstacles.
Choosing the right sensor depends on the application, environment and required detection behavior.