By Allan B. Colombo
Copyright©1988,1999, 2002
Let us begin by learning the difference between the various types of locks on the market. Figure 1 shows us the usual key-in-knob lock found on most residential doors. A key must be used from the outside, while a convenient push or turn button is used from the inside. The place of metal protruding into the door frame is commonly called a latchbolt, and in a key-in-knob lock usually extends 3/4 in. into the frame. The security of a door protected by a key-in-knob lock alone is questionable.
Some key-in-knob locks used a positive locking feature called deadlatching, which uses a small latch that runs alongside the latchbolt. When the latchbolt is extended and deadlatching takes place, the latchbolt cannot be jimmied by using a credit card or screwdriver. The use of a key is the only way this latch will release. Deadlatching has greatly improved the composite security of the key-in-knob but is not the only answer.
Dead bolt locks, on the other hand, offer more protection. The dead bolt will extend, at a minimum, one inch into the strike plate. Some manufacturers have even designed their dead bolt lock so the steel bolt extends up to two inches into the strike plate. In addition to this longer bolt, there is often a hardened steel shank placed through the center, making sawing and prying even more difficult. You can identify this type by looking at the end of the bolt. You will usually see the rounded end of the shank. A dead bolt usually has a deadlatching feature that takes place whthin the lock mechanism itself. A key is necessary to unlatch the dead bolt machinery.
Figure two illustrates the single- and double-cylinder ded bolt locks. Both locks have the same one- to two-in dead bolt but differ in how they lock and unlock from inside the house. The single-cylinder model has the typical key-operated mechanism on the outside and a convenient turn knob on the inside. The double-cylinder model requires the same key be used on the outside and inside cylinders alike.
The advantage of a double-cylinder over a single-cylinder is that the burglar using a window for entry, for instance, will not find an easy egress through any door. The customer's VCR and portable TV in hand, he'll suddenly find himself face to face with a lock that requires a key. Now he'll have to exit another way...a window perhaps. The going will be more time-consuming, and maybe he'll change his mind and leave the house emty-handed--while he's still a free man.
Figure three shows a rim cylinder lock. This type of lock also comes in single and double cylinders. The rim cylinder mechanism comes in either a remlatch or a dead latch and is surface-mounted on any door. Outside, you have the typical key-operated cylinder and on the inside, the convenient turn button. Some rim cylinder locks even use double cylinders for even greater protection. When dealing with older, more vintage, doors, the rim lock will work very wll.
The cylinder of any lock is the mechanism that does the job of extending the bolt or retracting it. It also accepts or rejects any key that fits it. Entrance hinges on acceptance or rejection of the key.