A motion sensor attached to a light or an alarm system can protect your home from intruders. If your motion sensor light is acting up, first test it to find out why. Turn on the unit, then walk past the sensor in multiple directions to see if the light it controls comes on. If it doesn't, remove the light bulbs and test them individually. If the lights work, but the motion sensor doesn't turn them on, you'll know it's the motion sensor that is faulty. You can install a replacement sensor in just a few hours.
Locate the circuit breaker for the motion sensor and light. Turn off the power.
Determine if the motion sensor can be removed from the unit. Some models have removable sensors. In other models, the sensor and light are a single unit and you'll have to remove and replace the entire thing. If your model has a removable sensor, loosen motion sensor with a screwdriver.
Locate the wires protruding from the now-exposed portion of the unit. Typically there are three wires -- black, white and green or bare copper. Use a circuit tester to make sure no electricity is running through the wires before touching them. Detach the wires from the motion sensor.
Install the new motion sensor to the fixture, according to the steps described for your model. Connect the three wires you disconnected in Step 3 to the new sensor. Connect them in the same way they were connected to the broken motion sensor. Check the wire connections to make sure they're secure.
Tighten the motion sensor in place with a screwdriver.
Turn the power back on. Test the unit to see if the motion sensor is working.
Keep the owner's manual for your motion sensor unit and the replacement motion sensor; the information differs by manufacturer.
Use extreme caution whenever working with electricity. Even though you have turned off the power, use a circuit tester to make sure no electricity is running through the wires. If your project requires you to use a ladder, have someone act as a spotter.