How to Add a Peephole to a Door

Mark the spot on the inside surface of the door where you wish to mount the door viewer; this spot should be centered with respect to the horizontal measurement of the door. Measure the height of this mark from the bottom of the door, and record this height on a piece of paper. Measure the distance from the side edge of the door to the mark, and record this measurement. If only one person will use the door viewer, the mark should be at the same height as this person's eye level; if several people will be using this hole, the mark should be made at a height that is comfortable for everyone to use.

Mark the spot on the outside surface of the door by using the measurements recorded in the previous step.

Use a 3/32-inch drill bit to drill a small pilot hole halfway through the door from the outside surface. Use the same drill bit to drill a small pilot hole from the inside surface, and drill until the two pilot holes meet.

Drill into the exterior-side pilot hole with a drill bit that has the same diameter as the peephole. Drill halfway through the door. Use the same drill bit to drill halfway through the door through the interior-side pilot hole.

Insert the lens into the hole on the exterior side of the door. Insert the barrel into the hole on the interior side of the door. Hand-tighten the barrel against the lens. To ensure that the the barrel will not come loose from the lens, use a screwdriver to turn the barrel against the lens by placing the screwdriver head in one of the notches in the barrel and turning the barrel to tighten.