Installing a bedroom door lock is normally done for privacy rather than for security reasons. A popular option for a bedroom door is to fit a locking doorknob. Whereas exterior locksets are usually key-operated, privacy doorknobs are fitted with a central button on the locking side that is either twisted clockwise or pressed in to lock the door. Replacing an ordinary doorknob with the locking variety is simple; however fitting doorknobs to a new door that has not been drilled to accept hardware requires some expertise.
Measure 90 cm (36 inches) above the bottom of the door. Use the carpenter's square and draw a horizontal line with a pencil on both sides and edge of the door. Measure the distance from the edge of the door and mark the doorknob centre line as recommended by the manufacturer. If you are fitting locking doorknobs to a drilled and prepared new door or alternatively replacing the hardware on an existing door, you can skip ahead to Step 5.
Drill the large hole for the lock body with a 5.3 cm (2 1/8 inch) diameter hole saw. Since this tool won't reach all the way through, you must bore halfway through one side and then the other.
Mark the centre of the door edge on the previously marked line. Use the spade bit and drill a 2.1 cm (7/8 inch) latch hole horizontally through from the edge of the door to the lock body recess.
Use the latch plate as a template, slide the latch in and fit the plate. Mark the outline of the latch plate with a fine pencil. Remove the latch and carefully chisel out a square recess the same thickness as the latch plate. Test to see that it fits flush with the surface. Insert the latch, and with the latch plate as a guide, drill two screw holes using the Vix bit and secure with 2 of the countersunk screws provided in the doorknob kit.
Replace an ordinary doorknob with the locking variety by removing the securing screws on either side and sliding out the old doorknob, then remove the existing latch plate and latch mechanism. You can usually leave the old striker plate fitted to the doorjamb.
Inspect the locking doorknob and identify the parts; this consists of two halves that slide together and are attached with two long machine screws. Insert the locking half through the door and latch from the inside and align the centre latch spindle containing the locking mechanism so that the two halves slide together correctly. Attach both sides with the two long machine screws and tighten.
Read and understand the manufacturer's instructions on fitting the striker plate. Mark out its position on the doorjamb. Drill two overlapping 9 mm (3/8 inch) deep by 2.1 cm (7/8 inch) diameter holes in the centre of the doorjamb to accept the door latch. Chisel out the necessary square recess and secure the striker plate with the remaining screws provided in the doorknob kit.
Open and close the door and test the lock to ensure correct alignment and fit.
The larger home improvement outlets stock factory drilled doors ready to accept locking doorknob hardware. When marking both sides of the door with the doorknob centre line, tap a nail in to create a guide for the hole saw's pilot drill bit. The same applies to the 2.1 cm (7/8 inch) latch hole. When drilling the 2.1 cm (7/8 inch) latch hole, tape a small spirit level to the drill. Monitor the left-to-right and horizontal alignment carefully while drilling to avoid a sticking latch.