A dead bolt, deadbolt or dead lock is a locking mechanism distinct from a

spring bolt lock A latch or catch (called sneck in Northern England and Scotland) is a type of mechanical fastener that joins two (or more) objects or surfaces while allowing for their regular separation. A latch typically engages another piece of hardware on t ...

because a deadbolt can only be opened by a key or handle. The more common spring bolt lock uses a

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

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, as well as make the door more resistant to forced entry. A deadbolt is often used to complement a spring-bolt lock on an entry door to a building.

Common types

A deadlock, if it is cylinder operated, 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). Double cylinder locks are sometimes banned from areas because they can be difficult to open from the inside and violate

fire safety Fire safety is the set of practices intended to reduce the destruction caused by fire. Fire safety measures include those that are intended to prevent the ignition of an uncontrolled fire and those that are used to limit the development and eff ...

regulations. Some lock manufacturers also have a "lockable" knob: a key is always needed on one side (usually external), and a twist knob can be used on the other (internal), ''unless'' a button has been pressed, in which case a key is also needed on the internal side. A variant of the standard deadbolt is the vertical deadbolt, invented by Samuel Segal. Vertical deadbolts resist ''jimmying'', in which an intruder inserts a

crowbar A crowbar, also called a wrecking bar, pry bar or prybar, pinch-bar, or occasionally a prise bar or prisebar, colloquially, in Britain and Australia sometimes called a jemmy or jimmy (also called jemmy bar), gooseneck, or pig foot, is a tool ...

between the door and the

jamb A jamb (from French ''jambe'', "leg"), in architecture, is the side-post or lining of a doorway or other aperture. The jambs of a window outside the frame are called “reveals.” Small shafts to doors and windows with caps and bases are known ...

and attempts to pry the bolt out of the door. Other types of deadbolts include: * Classroom-function (thumb-turn only unlocks door) * Exit-only function (no external cylinder) * Push-button deadbolt (mechanical or electrical) * Single cylinder with removable thumb-turn

Safety

The double cylinder design raises a safety issue. 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. 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 one may be crawling to get to the exit, thus placing the key where it is easiest to find. Note that single cylinder dead locks (with an unlocked twist mechanism on the inside of the door) do not have this problem, and therefore are most commonly used on fire exits. Some areas have fire safety codes that do not allow a locked exit.

References

{{Locksmithing Doors Locksmithing Locks (security device)

Common types

Safety

See also

References