Motion Sensor Light Stays On and Won't Turn Off

Quick Answer

A motion sensor light that stays on constantly is usually in manual override mode (triggered by flipping the switch off and on quickly), has its sensitivity set too high, or is detecting a constant heat source like an HVAC vent or dryer exhaust. Resetting the sensor by turning off power for 30 seconds typically clears the override. Adjusting the sensitivity and aim solves the false-trigger problem.

The Override Mode Trap

This catches more people than any actual malfunction. Most motion sensor lights have a built-in manual override feature. If you flip the wall switch off and then back on within one to three seconds, the sensor enters override mode and keeps the light on continuously, ignoring the motion sensor entirely.

This is a deliberate design feature -- it lets you keep the light on when you want steady light without waiting for motion to trigger it. The problem is that people trigger it accidentally. A quick flip of the switch, a brief power interruption, or even a momentary outage can put the sensor into override mode without you realizing it.

The light then stays on all night, and you assume the sensor is broken.

How to Reset the Sensor

Sensitivity and Aim Issues

Motion sensors (specifically PIR sensors, which are the most common type) detect changes in infrared radiation -- heat signatures. When a person walks through the detection zone, their body heat creates a change that the sensor picks up. But other heat sources can trigger it too.

HVAC vents. If a heating vent blows warm air across the sensor's field of view, the moving warm air can trigger the sensor repeatedly. This is especially common with outdoor sensor lights mounted near a dryer vent or a heat pump's outdoor unit.

Vehicle traffic. A sensor aimed at a street or driveway can detect the heat from passing cars. If traffic is frequent enough, the sensor never gets a chance to reset.

Small animals. Cats, raccoons, possums, and even large rats can trigger a motion sensor. If you have wildlife activity at night, the light may appear to stay on when it is actually cycling through constant re-triggers.

Wind-blown objects. Flags, tree branches, or hanging decorations that move in and out of the sensor's field can trigger it, especially if sunlight warms them above ambient temperature.

Direct sunlight. A sensor that faces west and gets hit by afternoon sun can be overwhelmed by the infrared energy. The sensor may stay triggered as long as the sun shines on it, then work normally after sunset.

Adjusting the Sensor

Most motion sensor lights have two or three adjustable dials, usually accessible on the face or underside of the sensor housing:

Sensitivity (SENS). This controls how much of an infrared change is needed to trigger the light. Turn it down if the sensor is triggering from distant cars, small animals, or wind. Turn it up if the sensor is not detecting people until they are very close.

Time (TIME). This controls how long the light stays on after motion is detected. Settings typically range from 15 seconds to 20 minutes. If this is set to the maximum and the sensor gets even one false trigger within the timeout window, the light resets and stays on for another full cycle -- which can make it seem like it never turns off.

Lux / Daylight (LUX). This controls the ambient light level below which the sensor activates. At its highest setting, the sensor only activates in complete darkness. At its lowest, it activates even during daylight. If this is set too low, the sensor may activate during dusk or dawn when you do not want it.

When the Sensor Has Failed

If you have reset the sensor, reduced sensitivity to minimum, and aimed it away from all heat sources, and the light still stays on, the sensor itself may have failed. PIR sensors can fail in the "on" position due to:

Water intrusion. If the sensor housing is not fully weatherproof, moisture can short the sensor circuit, holding it in the triggered state.
Electrical surge. A lightning strike or power surge can damage the sensor electronics.
Age. After 8 to 12 years of outdoor exposure, UV degradation and thermal cycling can cause the sensor or its lens to fail.

Replacement sensor heads are available for many fixture brands for $15 to $30. If the sensor is integrated into the fixture and not replaceable separately, you may need to replace the entire fixture, which typically runs $30 to $80 for a basic motion-sensing floodlight.

A Common Mix-Up

Some homeowners do not realize that their motion sensor light is actually two separate components: a light fixture and a motion sensor add-on screwed into the same electrical box. The sensor may have its own switch or mode button. Check if there is a small button or switch on the sensor housing that has been inadvertently set to "ON" or "TEST" mode.

Similarly, some smart motion sensor lights have app-based controls. If someone in the household set the light to "always on" through the app, the physical sensor is being overridden by software. Check the app before troubleshooting the hardware.

If you are having broader issues with outdoor lighting, like a power strip clicking randomly or lights connected to a GFCI that keeps tripping, those are separate electrical problems worth investigating on their own.