How to replace a manual deadlock with a two-way keyed lock.
How to change a door lock
Q One of my doors has a lock with just a deadbolt on one side. How can I change it to a normal lock with keys, which can be locked from both sides?
A This is simply a matter of changing the lock barrel, rather than replacing the door handle entirely.
What you need
A lock barrel (readily available from hardware stores). Ensure that you buy the size that matches the thickness of your door, plus allows for a raised door-handle plate, if necessary.
A screwdriver (check the existing screws to see which type you need)
A small Allen key
Step 1 Remove the screws from the existing handle-plates on both sides of the door. Then loosen both of the handles using a small Allen key or screwdriver. The screw or Allen bolt will usually be underneath the handle, so you can turn the handle to make it easier to reach.
Step 2 Once the handles are loosened, pull them out of the door from both sides. The metal bar through the door is what the handles will reattach to later. The deadlock and the deadbolt activator are still attached to the handle plate. Detach them by unscrewing the large screw at the end of the barrel. The deadbolt barrel will have left a hole in the door where the new lock barrel will go.
Step 3 Place the new lock barrel into the hole. The hole underneath the deadbolt is where the holding screw will go; it will screw into the lock barrel to hold it in place. You may need to adjust the new barrel slightly to the left or right until the holding screw can be fully screwed in.
Step 4 Replace the door handles on both sides, re-tighten the handles using the Allen key, and replace all of the handle-plate screws. Turn the handles to make sure the movement is normal, then use one of your keys to lock the door and check that the lock bolt is extending properly.