Installing a motion detector: indoors and outdoors

The motion detector, also called a presence detector, automatically switches on a light when a person enters its detection range. Handy in a hallway, garage, entrance or outdoors, it avoids fumbling for a switch in the dark and deters intruders. Its installation requires an electrical connection at 230 volts: it is within reach of a careful DIYer, provided you switch off the power, check there is no voltage and follow the wiring. Here is how to choose, install and adjust your detector properly.

Choosing your motion detector

• The passive infrared detector (PIR): the most common, it detects the heat of moving bodies and uses very little power
• The microwave or ultrasonic detector: sensitive to movement, it can pass through some obstacles but may trigger false alarms
• The detection angle: from 120° to 180° depending on the model, to be matched to the location and the area to cover
• The range: generally 5 to 8 metres, depending on the mounting and the height
• Outdoors, a minimum IP44 protection rating is recommended, and IP55 or more if the detector is exposed directly to the rain
• The detector can be built into the floodlight (standalone unit) or wired to an existing lighting point

How a PIR detector works

The passive infrared detector analyses variations in infrared radiation within its field of view: the passing of a person, whose body heat is far higher than the surroundings, triggers the switching. It is designed to ignore slow changes (the sun warming a wall), which limits false alarms outdoors. A motion detector is generally powered at 230 volts and controls one or more lighting points. The standard connection involves three conductors: the live wire, the neutral and the lamp return, and the wiring must strictly follow the diagram supplied with the device.

The step-by-step installation

1. Switch off the circuit breaker for the relevant circuit at the consumer unit and check there is no voltage with a non-contact tester
2. Identify the three wires: the supply live, the neutral and the return wire to the light fitting
3. Strip the conductors to 8 to 10 mm and connect them to the detector respecting the markings (L, N and the lamp output)
4. Fix the detector at the height recommended by the manufacturer, generally between 1.80 m and 2.50 m from the floor for good range
5. For an outdoor mounting, ensure the connection is watertight and use properly tightened cable glands
6. Switch the power back on and test: the detector must trigger the lighting as soon as you enter the zone
7. Adjust the orientation of the detector head to cover the area you want without aiming at the street or the neighbour's house

The adjustments: timer, brightness and sensitivity

• The timer: how long the light stays on after the last movement detected, usually adjustable from a few seconds to 10 minutes
• The brightness threshold (lux): the detector only activates at night if the ambient brightness is below a threshold, useful outdoors
• The sensitivity: reduce it if false triggers multiply (animals, trees)
• Indoors, position the detector along the direction of travel rather than facing a window that would cause heat variations
• After adjusting, check the behaviour in real conditions in the evening, when the light drops

The mistakes to avoid

• Working without switching off the power and without checking there is no voltage
• Confusing the live wire and the lamp return wire when connecting
• Installing a non-waterproof indoor detector outdoors
• Mounting the detector too low: the range and detection angle are reduced
• Using incompatible bulbs (some low-load LEDs can behave badly with the detector)

A well-chosen and properly installed motion detector brings comfort, security and savings: the light no longer stays on by mistake, and the outside of the house lights up automatically when someone approaches. The key points are working with the power off, following the wiring diagram scrupulously and choosing a model suited to the installation spot. If your circuit has no neutral wire or if you have any doubt about the wiring, an electrician can carry out the installation in a few dozen minutes for a moderate cost.