A deadbolt or deadlock, is a locking mechanism distinct from a spring-bolt lock because a deadbolt cannot be moved to the open position except by rotating the lock cylinder. The more common spring-bolt lock uses a spring to hold the bolt in place, allowing retraction by applying force to the bolt itself. A deadbolt can therefore make a door more resistant to entry without the correct key.

A deadbolt is often used to complement a spring-bolt lock on an entry door to a building.

Common Types

A deadlock may be either single cylinder or double cylinder. A single cylinder deadlock will accept a key on one side of the lock, but be operated by a twist knob on the other side. Double cylinder locks will accept a key on both sides and can therefore do away with the twist knob. This prevents unwanted unlocking of the door by forced access to the twist knob, via a nearby window for example.

A variant of the standard deadbolt is the vertical deadbolt, which generally rests on top of a door. Vertical deadbolts resist jimmying, in which an intruder inserts a pry bar between the door and the frame and attempts to pry the bolt out of the jamb.

Other types of deadbolts include:

• Single Cylinder with removable thumbturn
• Classroom Function (thumbturn only unlocks door)
• Exit Only Function (no external cylinder)
• Pushbutton Deadbolt (mechanical or electrical)

Security Considerations

Many designs are available from manufacturers. Various manufacturers have patented designs offering unique solutions to prevent the locks from being defeated by picking, lock bumping, prying, and other forceful attacks.

A deadlock can provide more security than an ordinary spring-bolt lock simply because of the weight of the locking bolt. Since the bolt in a deadlock does not need to retract quickly like a spring-bolt does when closing a door, it can be heavy, allowing for stronger designs.

A double cylinder deadlock without a twist knob cannot be opened without a key. This design may be suitable for doors with glass sections, or doors with nearby windows, since a deadlock with an internal twist knob may be opened by penetrating the nearby glass and reaching the knob. This double cylinder design raises a safety issue however. In the event of a fire, occupants will be prevented from escaping through double-cylinder locked doors unless the correct key is used. This is often an avoidable cause of death in house fires. The risk can be mitigated by locking the deadlock only when there are no occupants inside the building, or leaving the key near the keyhole.

See also

• Door security
• Lock bumping

External links

• Locking up tight with a deadbolt
• Deadbolt in a residential use