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A dead bolt or dead lock (also deadbolt), 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 is operated by a twist knob on the other side. Double cylinder locks will accept a key on both sides and therefore do not require (and often do not have) any twist knob. This prevents unwanted unlocking of the door by forced access to the interior twist knob (via a nearby window, for example).^[1]

A variant of the standard deadbolt is the vertical deadbolt, invented by Samuel Segal. Vertical deadbolts resist jimmying, in which an intruder inserts a pry bar between the door and the jamb and attempts to pry the bolt out of the door.^[2]

Other types of deadbolts include:

Single Cylinder with removable thumb-turn
Classroom Function (thumb-turn only unlocks door)
Exit Only Function (no external cylinder)
Push-button Deadbolt (mechanical or electrical)

Security considerations

A deadlock can provide more security than the spring bolt lock for a number of reasons.

One must have a key to open the door. This discourages intruders since the easy "just open the door" option is unavailable; they cannot hope for a quick getaway, e.g. if they find the premises are occupied.

There are techniques of opening a spring bolt door that work by using a suitable implement to push on the bolt. As the bolt is only held in place by a spring, the force required to open it is within reach of a blade similar to a paint chipper.

But with a deadlock, it would take a serious amount of force to cause the bolt to move without the key, and this force is considered impractical to deliver ... the practicality is that it would be easier to just attack the door with the aim of removing the lock, or removing the door off its hinges, or removing the door jamb, than to aim to move the bolt of the deadlock.

The 2nd type of lock, with perhaps a second method of picking, possibly a far smarter lock design than the standard tumbler, would make it more obvious that the lock pick was not using a key to open it, thus exposing the lock pick to being identified.

As the door is only locked by using a key, and it can only be locked when it is closed properly, closing the door and ensuring it is properly closed and locked becomes a habit . With doors that can be locked before being closed, or spring bolt locks, the bolt may fail to engage the door jamb due to forgetfulness, misalignment, obstruction or malfunction.

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.

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.

Safety

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.^[3] 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. Some fire departments suggest putting the key on a small nail or screw near the door at floor level, since the cleanest air is at floor level and you may be crawling to get to the exit, thus placing the key where it is easiest to find.

References

^ Deadbolt Locks - Electronic Locks. Askthebuilder.com. Retrieved on 2010-11-16.
^ urban Firefighter Vertical deadbolt
^ Deadlocked doors seen as fatal in house fire - National. www.smh.com.au (2004-06-08). Retrieved on 2010-11-16.

External links

[1] Deadbolt Locks - Electronic Locks. Askthebuilder.com. Retrieved on 2010-11-16.

[2] urban Firefighter Vertical deadbolt

[3] Deadlocked doors seen as fatal in house fire - National. www.smh.com.au (2004-06-08). Retrieved on 2010-11-16.

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@@ Line 25: / Line 25: @@
 * One must have a key to open the door.  This discourages intruders since the easy "just open the door" option is unavailable; they cannot hope for a quick getaway, e.g. if they find the premises are occupied.
-* There are techniques  of  opening a spring bolt door that work by  using a suitable implement to push  on the bolt. As the bolt is only held inplace by a spring, the force required to open it is within reach of a blade similar to a paint chipper.
+* There are techniques  of  opening a spring bolt door that work by  using a suitable implement to push on the bolt. As the bolt is only held in place by a spring, the force required to open it is within reach of a blade similar to a paint chipper.
 But with a deadlock, it would take a serious amount of  force to cause  the bolt to move without the key, and this force is considered impractical to deliver  ...   the practicality is that it would be easier to just attack the door with the aim of removing the lock, or removing the door off its hinges, or removing the door jamb,  than to aim to move the bolt of the deadlock.