Deadbolts can be keyed on one side with a turn knob on the other, keyed on both sides, Keyed or turn knob on one side only. Your bolt should extend at least 1 inch from the edge of the door. Many older deadbolts have a much shorter "throw" and it is not enough to prevent the door from being pried open. Deadbolt strength is dependent upon the strength of the JAM, or what the bolt goes into. Jams can be reinforced with many products to make it much more difficult for intruder to bypass the lock. http://www.evergoodlocks.com/mechanical-lock/