How to Install a Security Chain on a Door. Standard door knob locks do little to keep out a crafty criminal. You may need to install a security chain on a door to keep your family and belongings extra safe. Chain locks allow you to open a door partially to see who's there instead of greeting strangers and potential predators with doors wide open. They are also much harder to force open than normal locks.
Go shopping. Visit your local hardware store or locksmith and see what they have to offer. Don't be afraid to ask an employee for help. Try to find a chain with a template for installation.
Gather needed materials. Take the lock out of the package and read the instructions to see what kinds of screwdrivers or drill bits you'll need. Also, get a pencil and some masking tape.
Tape up the template for the lock plate. This is the part that is not attached to the chain. Position it about 3 to 6 inches above the deadbolt on your door. If you do not have a deadbolt on the door, place it about three to six inches above the door handle.
Mark the points on the template with the pencil. The template should make it clear where you need to mark, but check the instructions to be sure. After you have the door marked you can take the template down.
Pre-drill the holes for the screws. Make sure you have the proper bit. Drill holes into the appropriate markings.
Screw the lock plate onto the door.
Tape up the template for the chain mount. (There should be a different template for the chain mount.) Position it on the wall just outside the door frame. Make sure it lines up with the lock plate.
Mark the template, just as you did the first one.
Pre-drill the holes for the chain mount, as you did in Step 5.
Screw in the chain mount.
Test it out. Make sure the lock is secure and can't be unchained from the outside. The door should open no more than an inch when it is chained.