Many homeowners have old doors somewhere in the house that they no longer have the keys for. If these doors are locked, it can be difficult to remove the lock and replace it with a unit that works. If you are able to gain access to the interior of the room through a window or some other means, this is usually the easiest way to remove the lock. If no access is available, you'll usually have to rely on some more extreme methods of removing the lock.
Removing Locks From the Interior Side
Open the door and look for the latch plate along the door's edge. Unscrew this plate and remove the latch from the door, if possible.
Look for a small set screw at the base of the handle. Remove this screw using a drill or screwdriver. Grasp the interior trim in one hand and the exterior trim in the other and try to pull them away from the door. Often, this set screw is the only thing holding the two halves of the lock in place.
Examine the handle and trim on the interior side of the door. There may be a small pinhole holding the handle in place. Insert a straightened paper clip into this hole and apply pressure to release the interior handle. Insert the pin straight through the lock cylinder to reach the lock's release mechanism. Once you trigger this release, you'll be able to pull the lock apart by hand.
Pry the trim from around the handle or lever using a flat screwdriver. Some trim may even twist off by hand. Look for screws hidden underneath. Remove these screws, then pull the two halves of the lock apart to remove them from the door.
Check for small notches or depressions in very old door knobs. Slip a screwdriver in to release the knob, which will expose a length of wire wrapped around the remaining trim. Press this wire with your screwdriver to release the interior half of the lock, then pull the exterior half off by hand.
Removing Locks from the Exterior Side
Check for any pinholes or depressions in the handle or around the trim. Some locks designed for interior use may have these holes on the exterior side for homeowners who have lost the key. Slip a straightened safety pin into small holes, or use a flat screwdriver to press against a slot or depression. This will release the handle and may expose screws underneath. By removing these screws, you may be able to remove the lock and open the door.
Take the door off its hinges. Use a hammer and center punch to drive out the hinge pins, if they are accessible. Once the door is no longer connected to the frame, you'll be able to slip it out of the opening and remove the lock from the interior side.
Drill out the lock cylinder. Use a sharp drill bit that is designed for metal drilling. Aim the drill into the area just above the keyway. The goal is to drill through the pin tumblers, not the keyway itself. Once you've drilled through and broken the pins, you may need to insert a flat screwdriver to retract the latch and open the door. From here, you'll be able to remove the lock using the techniques listed in Section 1.