What is a motion sensor and how does it work?
A motion sensor detects movement in a room and sends a signal to your smart-home system. Most sensors used in the home — such as the Philips Hue Motion Sensor or Google Nest-compatible models — are based on passive infrared (PIR) technology. This means the sensor does not emit any radiation, but instead picks up the infrared light that people and animals radiate as body heat.
As soon as the sensor registers a sudden change in the infrared pattern — you walk through the room — it fires a trigger. That trigger can be linked to automations: lights on, heating up, a notification on your phone.
Some newer sensors combine PIR with radar technology (such as the Google Nest Hub 2nd gen or the Aqara FP2). Radar can detect even subtle movements like breathing, which is useful when you want to know whether someone is sitting still in a chair.
The ideal placement: height, angle and position
Where you mount a motion sensor accounts for 80% of how well it performs. Poor placement is the single biggest cause of frustration: lights that don't turn on, or that switch off far too quickly.
Optimal mounting height
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2 to 3 metres is the sweet spot for PIR sensors in a living space.
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Too low (below 1.5 m): the sensor detects pets as people and triggers constantly.
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Too high (above 3 m): the detection angle narrows and you miss movement close to the walls.
Detection angle and orientation
Most PIR sensors have a detection range of 90° to 120° horizontally. Point the sensor perpendicular to the direction people walk — not parallel to it. Walking across a sensor's field of view produces a much greater infrared change than walking straight towards it.
Where possible, place the sensor in a corner of the room so it has a clear view of the entire space. In a hallway, a sensor at the end works better than one mounted on the side wall.
Avoid these locations
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Direct sunlight or near radiators: heat sources cause false-positive detections.
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Behind glass: infrared does not pass through glass.
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Above air-conditioning vents: airflow can fool PIR sensors.
Step by step: setting up a motion sensor
1. Choose the right spot Use the guidelines above. Not sure? Hold the sensor temporarily in the intended position and walk around the room before you reach for a drill.
2. Mount it securely A sensor that wobbles or tilts will give inconsistent results. Use a solid wall bracket and make sure it is firmly fixed. Depending on the surface, you can screw the bracket in place for maximum stability or, if preferred, attach it with strong double-sided tape. The KANN wall brackets for the Philips Hue Motion Sensor are designed for stable, adjustable mounting — making them a practical solution for rental homes where drilling is not always possible or permitted.
3. Pair it with your system Add the sensor through the relevant app (Philips Hue app, Google Home, Apple Home). Follow the pairing steps in the app; this usually takes less than two minutes.
4. Set sensitivity and timeout Most apps let you adjust the sensitivity (how small a movement needs to be to trigger the sensor) and the switch-off delay. Start with a delay of 3 to 5 minutes for a living room, and 1 minute for a hallway or bathroom.
5. Create the automation Link the sensor to a scene or action. Some examples:
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Hallway: light on when motion is detected, automatically off after 2 minutes.
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Home office: light on and do-not-disturb mode on your phone when presence is detected.
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Bedroom (night): dim the light to 5% when motion is detected between 11 pm and 6 am.
Common mistakes (and how to avoid them)
Timeout set too short A delay that is too brief means the light turns off while you are still in the room. Increase the delay or use a sensor with presence detection.
One sensor for a large room You cannot cover an open-plan living room of 40 m² with a single sensor in one corner. Use multiple sensors or choose a model with a wider range.
Forgetting to recalibrate after moving the sensor Have you repositioned the sensor? Reset your automations and check the sensitivity again. The environment changes along with the sensor's new vantage point.
Sensor on a flat wall instead of a corner Mounted on a flat wall, a sensor covers at most half the room. Turning it into a corner effectively doubles the detection area.
Combining a motion sensor with other smart devices
A motion sensor becomes truly powerful when paired with other devices:
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Smart lights: the most obvious combination. Link to Philips Hue groups for consistent scenes.
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Smart thermostat: activate a heating zone only when someone is in the room.
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Smart speakers: play a welcome message or start a playlist automatically.
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Security cameras: use the sensor as a recording trigger instead of recording continuously.
Bear in mind that motion sensors run on batteries in most consumer models. Check the battery level regularly through the app and replace batteries proactively — a dead battery at the wrong moment is always inconvenient.
Ready to mount your sensor properly?
A great sensor starts with a great mount. At KANN you will find 3D-printed wall brackets, stands and accessories for popular motion sensors from Philips Hue and other brands — clean, sturdy and easy to install with screws or double-sided tape. Browse the range in the KANN shop and give your smart home the finish it deserves.