Dead bolts are essential for all entry doors. Their effectiveness can be greatly decreased, however, if not installed properly.  To check your dead bolt open your door and turn your key until the throw is fully extended.  Notice the placement of the key when the dead bolt is in the locked position.  Repeat this action when the door is shut and compare the results. Without taking this safety precaution a dead bolt could be easily be manipulated.  Check, also, that the throw (the piece that extends into your door frame) is at least one inch in length.  In older homes this can be as little half an inch.

Installation

If your lock is not installed properly you may not be benefiting from all of the security it has to offer.  Install the striker with screws that are long enough to actually pass through the frame and into the stud beside it for added support against kick-ins.

All exterior doors should have a solid core.  A lock can only be as strong as your door.  Inferior doors can more readily be destroyed than solid ones, thus making even a quality lock completely ineffective.  Getting into your dwelling should be as difficult and unattractive as possible to unwanted intruders.