Deadbolt locks are one of the easiest ways to boost home security. A deadbolt is more difficult to defeat than a simple locking knob, so it makes it more difficult for someone to break into a home, business or storage space. Installation of a deadbolt would normally require cutting a pair of holes in the body of a metal or wooden door; however, removing an existing lock and installing a new one takes advantage of the cuts that are already in place.
1 Before removing the old lock, measure the door to determine the configuration needed in the replacement lock. First, measure and record the thickness of the door. Second, measure and record the backset of the existing lock. The backset is the distance from the edge of the door to the center of the lock, measured on the face of the door. There are two standard backsets for residential locks: 2-3/8 and 2-3/4 inches. If the backset is not one of those two sizes, you may need to special-order a replacement lock.
2 A deadbolt consists of two halves that form a "sandwich" around the door, with the workings of lock in a large hole hidden by the faces of the lock. [reference 1, 2] The two halves are held together by screws that can only be reached from inside the building. Loosen these two screws entirely and the two halves of the lock should pull free. If the current deadbolt is a single-cylinder lock with a thumb knob on the inside, the screws are usually hidden by a cover. Remove the thumb knob, which is held in place by a set screw, and then pull off the cover to find the screws. Depending on the brand of lock, the outside cylinder may be held in place by screws that are only visible after the inside half of the lock is removed. The bolt is held in place by screws that fasten a face plate to the door's edge. Remove the screws and pull the bolt and its works straight out of the edge.
3 Take the old lock to the store to buy a replacement. Check the packaging to make certain that a new lock can fit the thickness and backset you measured. When buying the new lock, look for one with the same screw positions and configuration as the face plate and strike plate of the old lock. That will reduce the need to drill new holes in the door and door jamb.
4 Follow the manufacturer's instructions to install the new lock, making certain to put the thumb knob on the inside surface. Many new locks can be adjusted for either backset, and their packaging will include instructions for changing from the default backset. If the lock is a double-cylinder deadbolt, which requires a key to open from either side, be sure to put install it with the screws on the inside.
5 Close the door and throw the bolt to see whether it engages securely with the old lock's strike plate. If it doesn't, remove the old strike plate. Before installing the strike plate that came with the new lock, verify that the bolt can extend to its full length in the door jamb. If it does not, you will need to drill the receiver hole deeper. Install the new strike plate and adjust its position so that the bolt engages easily and securely.