Tools you will need:
circuit tester, screwdriver, wire strippers/cutters, electrical tape
First: Identify the room where you want to install the motion sensor light switch to replace a normal wall light switch. Keep in mind that the motion sensor light switch picks up motion moving across the sensor. Any room with a light switch will work, with most people adding motion sensor switches to garages, closets, pantries, foyers or hallways as their 'first' room. Depending on the sensor switch you have, you will be able to set the amount of time that your light stays on after motion is detected. Activation of the light will take place when someone walks into the room.
Second: Turn off the electricity to the light switch you will be working with. If your circuit box is not properly marked to identify which circuit corresponds with your switch, then use this method: Turn the switch so that the light in the room turns on. Then, go to the circuit box and, one switch at a time, turn of the circuits to see which switch controls the light switch you are replacing. Mark the switch with a note that says 'leave off' or something similar, and let everyone in the house/building that has access to the circuit breakers know that you have turned off the circuit and that they should not turn it back on.
Third: With the circuit off, go back to the room with the light switch you will be replacing. Using a flathead screwdriver, unscrew the screws (usually two) connecting the existing faceplate, and remove the faceplate by pulling it out. With the faceplate off, remove any remaining screws holding the switch to the electrical box, and pull the switch out of the electrical box (the wires will remain attached to the switch when you pull it out). You will want to pull the switch out approximately 2 to 3 inches.
Fourth: Using the circuit tester (read the directions that come with the circuit tester if you aren't familiar with its operation), test the wires connected the the existing light switch to make sure the power is off. Better safe than sorry! Normally, this is accomplished by touching one probe of the tester to the ground wire from your electrical box, and touching the other probe of the circuit tester to one of the other wires connected to your existing light switch. If the wires are not live and the electric is not on, then This can be done by touching one probe of the tester to the ground wire and touching the other probe to one of the other wires. If the wires are not live and you have confirmed that the power is off, disconnect the two wires (will likely both be black wires) that connect to the existing light switch.
Fifth: Examine the electrical box and the existing wires inside of it. There will likely be (should be) two black wires and one ground wire, with the ground wire identifed by having a green coating or being just a bare copper wire. Re-read the instructions that came with your new motion sensor light switch, and confirm from the directions how the wires will connect to your new light switch. If you find that the wires in your electrical box don't make sense or match up to what you expected, stop. Either consult a professional or someone who is familiar with wiring and may be able to help you, or reassemble your old light switch back how it was until you can figure out how to proceed.
Sixth: For each wire in your electrical box, check the ends of the wires to confirm that they are not worn and that they do not have built up carbon deposits. If they do, then cut them back and strip off approximately 3/8 inch of coating to expose new bare wire that you will be using. NOTE: If your home has aluminum wiring, then it is critical that you use the proper connectors and steps when handling aluminum electrical connections. Proper aluminum wire connecters are required, and consulting a professional is highly recommended.
Seventh: Using a wire nut (or 'wire connecter'), which will likley come with your new motion sensor light switch, connect the existing wires from your electrical box to the corresponding short wires coming from the back of your motion sensor light switch. Tighten the wire nut until the connection is secure. Using electrical tape, wrap the tape around the wire nut connector and onto the wire that enters the wire nut connector for added connectivity.
Eighth: Push all of the wiring back into the electrical box in the wall. Using your scredriver, screw in the screws holding the switch and the faceplate (if your new switch has a separate faceplate). Once again, re-read the instructions to adjust your new motion light switch to the settings you want for your room.
You (should be) done! Turn the power back on and test your new motion light switch. I say you 'should be' done because, trust me, it's not unusual that you may have to turn the power back off, and trouble shoot what you have done to determine why the switch isn't working. Don't worry--take your time and walk through the steps and instructions for your new motion sensor light switch.
I hope you find these instructions helpful.