Begin by removing the screws from the door knob on the interior side of your door.
How to fit a internal door lock.
Open the door and stand with your back to the hinges.
Remove the two screws from the latch plate on the edge of the door and remove the latch from the opening.
This video is about how to fit a door latch and door handle in an interior door.
If the doorknob is on the left you need a left handed door.
If you re installing a pre hung door make sure you get the correct swing determined by the placement of the hinges and doorknob.
First mark out the place where the strike plate has to be fitted.
Create a mortise for the plate around the latch on your door using the technique described above.
Hold the door latch against the face of the door flush with the door edge and mark the spindle centre on your previously marked centre line see fig 1.
Create a mortise and holes for your lock and door handle.
Purchase a door stop or professional grade door wedge from a local hardware store or from an online retailer.
This allows you to pull the door knobs off the door from both sides.
Fit the wedge into the bottom of the door as close to the wall as possible.
In some cases door latch plate mortises might need to be cut or enlarged.
Then use a drill to make the necessary holes for installation of your doorknob door handle and lock.
If the knob is to the right select a right handed door.
This process will vary somewhat based on the doorknob you are installing.
Place a wedge at the bottom of the door to keep it in place.
Turn the key so the locking bolt protrudes from the lock and hold the door against the door frame.
Tools needed for this job.
Mark out the strike plate on the door frame after you ve fitted the lock in the door you need to fit the strike plate to the door frame.