When checking the security of your doors, the door itself and the hinges, locks and other hardware must be considered. Check for these features. These locks can be forced by breaking off the knob, and frequently they can be opened by prying or slipping a piece of plastic, such as a credit card, between the jamb and the bolt. The best defense for a good metal or solid core wood door is a deadlock with a one-inch throw bolt. If there are no windows in or near the door, the bolt may be operated from the inside by a thumb turn.
Outside operation can be by key or combination.
When installing a deadbolt, attach the strike plate to the door with three inch brass wood screws. The screws should penetrate through the frame to a structural member. If your door has glass panes or if there are windows within forty inches of the lock, a double cylinder deadlock is recommended, so that a key is required from either side of the door. The jimmy-proof deadlock shown below can be used on any hinge door where the strike can be securely fastened to the door frame. These locks come in double cylinder and inside thumb operated models.