Why does my sensor light stay on or keep turning on all night?

Most sensor lights use passive infrared, which reacts to warm things moving across its view. At night that includes cats, dogs, possums and moths, plus shrubs and branches moving on a windy night. An air conditioner's outdoor unit, a heater flue or a car parked after a drive puts warm air in front of the sensor, and a spider web across the lens can trigger it every time it moves.

Distance counts too. A sensor aimed across a footpath or driveway picks up people and cars passing the house. If it triggers more often than anyone walks past, the range is probably set too wide or the head is aimed too far out.

Most sensors have dials for run time and sensitivity. A run time turned to maximum keeps the light on long after each trigger, and frequent triggers keep restarting the timer, so it never gets to switch off. Many models also have a manual override, often turned on by flicking the wall switch off and on quickly, which holds the light on until it's cancelled. Turning the wall switch off for a minute and back on usually returns it to sensor mode, but check your model's instructions.

If the light stays on with nothing moving, after you've cleared the override and turned the sensitivity down, the sensor may have failed on, or water may have got into it. A fitting with water or condensation inside, or one that trips the safety switch, shouldn't be used. Replacing a sensor or fitting is electrical work for a licensed electrician.