Check to make sure the motion-sensing outlet is turned off. Plug it into a regular electrical outlet. Check the label of the motion-sensing outlet for the range of detection. Ensure the detection range covers the area where you want movement to trigger the light string.
Connect a heavy-duty extension cord to the regular outlet and run the cord to the detection area if the regular outlet is not near your desired detection range. Plug the motion-sensing outlet into the extension cord. Many motion-sensing outlets require a grounded plug, so make sure your extension cord is grounded. A grounded extension cord has three prongs instead of two.
Plug a string of lights firmly into the motion-sensing outlet. Turn the motion-sensing outlet on. Test the setup by waving your hand around in front of the motion sensor. If the lights come on, everything is set up correctly. Turn the sensor off again.
Hang the light string where you want it. If you put the lights outdoors, protect the motion-sensing outlet and extension cord from moisture. You can use plastic and waterproof tape to wrap the equipment, but do not obscure the motion-sensing component. Turn the motion-sensing outlet on again and test it once more to make sure it is set up correctly.