Now you need a drill machine to make a hole. Make sure that you use suitable drill bit before drilling, for that you must read guidelines provided on the machine pack.
Done with the instructions? Now drill a hole as per marked location and of perfect size drill bit.
Now hold the drill machine at right angle to the door and then begin drilling by using slow speed and little pressure.
Note: To avoid the breakage to the external part of the door, stop and ensure your movement. By doing so you will recognize when the direct tip first emerges.
Now open your kit and unscrew the door viewer into two parts. From the outside insert lens through the door.