Step One: What You Need
You'll need a surface-mounted lock, a pencil, a utility knife, and a power drill with screwdriver bits. You can buy the lock of your choice at your local home improvement center or hardware store.
Step Two: Get It Situated
Position the lock on the door at the height you want and mark the holes with a pencil. Place the receiver of the chain or bolt on the doorframe trim and lightly trace the outer edges in pencil. Use your utility knife to cut away the door trim [which is door trim and which is doorjamb? (The trim dresses the door jamb)] until you reach the doorjamb. Replace the lock piece and mark the screw hole in pencil.
Step Three: Lock It In Place
Use your drill and a bit that is slightly smaller than the mounting screw. Drill shallow holes at all the pencil marks. These are your pilot holes for the screws. Align the lock with the pilot holes and use your screwdriver to place and tighten all the screws (never overtighten, or you will strip screws.
You've added a level of safety to your home. And you did it yourself! For more fix-it advice, read my book “Room for Improvement.”