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What Is a Motion Sensor?
A motion sensor detects movement in a space and sends a signal to your smart home system. It's the most fundamental βsenseβ a smart home can have β without one, lights must be controlled manually, automations are limited to schedules only, and your security system can't βseeβ anything.
Detection Technologies
PIR (Passive Infrared) β The Classic
The most widespread technology. A PIR sensor detects changes in infrared radiation β essentially the heat emitted by a body in motion. Advantages: extremely low power consumption (2+ year battery life), cheap, reliable. Disadvantages: detects only motion (not presence β if you're sitting still on the couch, it doesn't βseeβ you), affected by ambient temperature, false alarms in warm rooms.
mmWave Radar β The Revolution
The new technology changing everything. The mmWave (millimeter wave) sensor emits radio waves and measures their reflections. It detects even the slightest movement β breathing, heartbeat, micro-movements. Result: true presence detection, not just motion. Lights never turn off while you're sitting still. Disadvantages: higher power consumption (typically requires USB power), more expensive.
Dual-Tech (PIR + mmWave)
Some premium models combine both technologies. PIR detects initial motion (fast trigger), then mmWave takes over for ongoing presence detection. Result: rapid detection + zero false positives.
| Feature | PIR | mmWave | Dual-Tech |
|---|---|---|---|
| Detects motion | β Yes | β Yes | β Yes |
| Detects presence | β No | β Yes | β Yes |
| Power Source | Battery (2+ years) | USB (continuous) | USB (continuous) |
| Price | β¬8-25 | β¬20-50 | β¬30-60 |
| False Alarms | Moderate | Low | Minimal |
| Detects through walls | β No | β οΈ Partially | β οΈ Partially |
Best Models 2026
PIR Sensors
Aqara Motion Sensor P2 (β¬20-25): Zigbee 3.0, adjustable sensitivity, light sensor (lux), 170Β° detection angle, 7m range. Excellent Home Assistant integration. CR2450 battery lasts 5 years.
IKEA VALLHORN (β¬10-12): Matter over Thread, dual PIR sensors for wider field of view, built-in light sensor. Works without a proprietary hub via Matter. Outstanding value.
Philips Hue Motion Sensor (β¬40-45): Zigbee, adjustable daylight sensitivity, thermometer, magnetic mount. Premium but top-tier quality.
SONOFF SNZB-03 (β¬8-10): The cheapest reliable sensor. Zigbee 3.0, CR2450 battery, basic but works perfectly.
mmWave Presence Sensors
Aqara Presence Sensor FP2 (β¬45-55): The king of presence sensors. 24GHz mmWave, zone detection (knows which area of the room you're in), fall detection, WiFi. Works with HomeKit, Home Assistant, Alexa.
Aqara Presence Sensor FP1E (β¬25-30): The budget version of the FP2. mmWave, Zigbee 3.0, no zone detection but excellent for basic presence detection.
Everything Presence One/Lite (β¬30-40): Open-source mmWave sensor, ESPHome-based. Full Home Assistant integration, customizable, community-supported.
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Placement Strategy
Correct placement is the difference between a sensor that works perfectly and one that drives you crazy:
Placement Rules
- Height 2.0-2.4m: Ideal for PIR β too low loses range, too high loses accuracy
- Don't aim at windows: Sunlight and heat cause false alarms with PIR
- Don't aim at radiators: Heaters trigger PIR sensors
- Corner at 45Β°: PIR detects perpendicular movement best β place in room corners
- mmWave on ceiling: For room-level precision, mount the FP2 on the ceiling
- Away from pets: If you have cats/dogs, adjust sensitivity or use pet-immune sensors
How Many Do You Need?
For a typical apartment (80-100 mΒ²):
- Basic coverage (3 sensors): Living room, kitchen, hallway
- Full coverage (5-7 sensors): + bathroom, bedrooms, balcony
- Premium (PIR + mmWave mix): mmWave in living room + office (presence), PIR in hallway + bathroom + bedrooms (motion)
Top Automations
Automation #1: Auto Lights
The classic automation. Motion detected β lights ON. No motion for 5 minutes β lights OFF. With an mmWave sensor, lights never turn off while you're sitting still.
Pro tip: Use the lux sensor β if there's enough natural light, don't turn on artificial lighting.
Automation #2: HVAC Control
No one detected for 30 minutes β AC OFF / thermostat to eco mode. Someone returns β restore temperature. Saves 15-25% on heating/cooling costs.
Automation #3: Security System
Alarm armed β motion detected β siren + push notification + camera recording. A DIY alarm system that replaces expensive monitored services.
Automation #4: Night Mode
After 11 PM, motion in hallway/bathroom β lights at 10% warm white instead of full brightness. Doesn't wake up the rest of the household.
Setup Cost
| Scenario | Sensors | Cost |
|---|---|---|
| Budget (3 rooms) | 3Γ SONOFF SNZB-03 | β¬24-30 |
| Value (5 rooms) | 5Γ IKEA VALLHORN | β¬50-60 |
| Smart Mix | 2Γ Aqara FP2 + 3Γ Aqara P2 | β¬150-170 |
| Premium Hue | 5Γ Philips Hue Motion | β¬200-225 |
Final Recommendation
For beginners: Start with 2-3 IKEA VALLHORN (β¬10 each, Matter). Place in hallway, living room, kitchen. Set up basic light automations via Google Home or Apple Home.
For enthusiasts: Aqara FP2 in the living room (presence) + Aqara P2 in the hallway and bathroom (motion) + Home Assistant automations. The ideal balance of cost and capability.
For power users: Everything Presence One (ESPHome mmWave) in every room + zone-based automations + Blueprint sharing. Full customization, open-source, community-driven.
The motion sensor is the first βsenseβ every smart home needs. Without one, your home is blind.