Identify the circuit to the light switch you'll be replacing, and turn the power off at the circuit breaker.
As an extra precaution, place a "Do Not Touch!" sign on the outside of the circuit box so that someone else doesn't unwittingly restore power to the circuit while you are working.
Remove the wall-plate from the existing switch, and test the wires using a circuit tester -- such as the audible-alarm tester used in our demonstration -- to be absolutely sure there is no power flowing to the wires you'll be removing. With our audible tester, a continuous beep would indicate that there is still power. The tester verified that the power was off.
With the power turned off, remove the screws that hold the old switch in place.
The old switch has three wires connected at the back: a black wire, a white wire and a bare ground. The black and white wires will be connected to the new motion-sensor switch, but the ground will not be used.
Cut the wires at the back of the old switch.
With the ends of the wires stripped, they can be hooked up to the new switch. Wrap the end of the black wire around one of the wire connections on the back of the switch. Repeat with the white wire. Secure the wires with wire-connectors.
Note: With the particular sensor-switch used in our demonstration, it made no difference which power-supply wire went to which connection on the back of the switch. Either wire could go to either connection. Follow the wiring instructions that come with the switch you purchase.
Tuck the excess wire into the back of the switch box (Image 1).
Position the connected motion-sensor switch into the switch box.
Secure the switch with the mounting screws provided (Image 2).
Note the customizing controls for adjusting the sensitivity and timing of the light activation. On our switch, the bottom adjustment controlled when the lights come on after someone enters the room. The bottom determines how long the lights stay on after everyone has left the room. Set these controls to your liking before installing the wall-plate (Image 1).
With the switch installed and adjusted, reinstall the switch wall-plate (Image 2).