Short answer
An ordinary motion sensor sees a moving difference in heat. That is why it also reacts to a cat, to warm air from a grille and to a branch in the sun. Mount it at about 2.20 to 2.50 metres, aim it across the walking direction, and set the three dials: sensitivity, time and dusk setting.
Who this article is for Anyone with a motion sensor that misbehaves. You can often adjust it yourself; mounting and connecting is installation work.
How it sees
An ordinary sensor is an infrared sensor: it sees a difference in heat that moves. That is why it works less well when someone walks straight towards it, and well when someone walks across its field of view.
That is straight away the most important tip: aim it across the walking direction, not along it.
The three dials
Almost every sensor has three, often under a cover:
LUX or the little moon. The dusk setting. Turn it towards the moon if it also triggers during the day. Adjust this in the dark, not during the day.
TIME or SEC. How long the light stays on after the last movement. For a back door one to two minutes is enough; for a drive longer.
SENS. The sensitivity and therefore the range. If it triggers on cats or a branch, turn it down.
Where it false-triggers
- warm air from a ventilation grille, a boiler flue or a dryer
- sunlight moving across a wall and warming it
- moving leaves reflecting the sun
- cars in the street if it looks too wide
- rain or snow at a very sensitive setting
Moving it helps more often than turning the sensitivity down.
Moving it helps more often than turning the sensitivity down, because turning it down means it also sees you later.
Where it should be mounted
- 2.20 to 2.50 metres high for a standard sensor
- across the walking direction
- not directly above the light it switches, because heat from the fitting can affect it
- for a drive slightly higher, with a larger range
Alternatives
For a long drive or a garden path a dusk sensor with a timer often works better: light on at dark, off at midnight, and a motion sensor as well for whoever comes home later.
For indoors in a hallway or toilet there are sensors that fit in the switch box, with a switching time of half a minute. That saves lights being left on all evening.
From my own work
At a home in Nuth the sensor by the back door came on about ten times every night. The customer thought it was cats. It turned out to be the warm air from the tumble dryer vent, blowing right past the sensor. Moved half a metre and it was over.
When to call an electrician
- The sensor switches on without anyone walking past
- It does not switch on when you walk up
- The light stays on or keeps going off too soon
This is usually a short visit in which I set it up properly straight away. Call +31 43 204 18 26.
Frequently asked questions
Why does my motion sensor switch on by itself?
Usually warm air from a grille, sun warming a wall or moving leaves. Moving it helps more often than turning the sensitivity down.
At what height is a sensor best mounted?
Around 2.20 to 2.50 metres, and across the walking direction rather than along it.
How do I set the dusk setting?
In the dark, not during the day. Turn it towards the little moon if it also triggers during the day.
Further reading
Installing outdoor lighting: what goes on underground
The light is the fun part, the cable the most important. Lay an empty duct now and you can extend later without digging.
The light is not working: check it yourself in four steps
Nine times out of ten it is the bulb, the lampholder or the switch. The tenth time it is a connection, and then you call.
Dimming LEDs: why they flicker, buzz or do not switch off
Almost every LED dimming problem comes from a dimmer made for incandescent bulbs. A new dimmer solves it.
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