Deadbolt
A lock type that requires a key or handle to open.
A deadbolt, also called a deadlock, is a lock set into a wooden door. It works by sliding a bolt into the door frame, and can be operated with a key from either side. Unlike a spring bolt lock, which uses a spring to hold the bolt and can be retracted by pushing on the bolt itself, a deadbolt can only be opened with a key or a handle. This design makes the door harder to open without the correct key and more resistant to forced entry. Deadbolts are commonly used alongside a spring-bolt lock on a building’s entry door.
There are several common types. A cylinder-operated deadlock may be single or double cylinder. A single cylinder deadlock accepts a key on one side and has a twist knob on the other. A double cylinder deadlock requires a key on both sides and usually has no twist knob, preventing someone from unlocking it by reaching an interior knob through a window. However, double cylinder locks are sometimes banned because they can be difficult to open from the inside, violating fire safety rules. Some manufacturers offer a lockable knob: a key is always needed on the outside, while the inside has a twist knob that can be locked with a button, requiring a key on that side as well. A vertical deadbolt, invented by Samuel Segal, resists jimmying, where a crowbar is used to pry the bolt from the door frame. Other types include classroom-function (thumb-turn unlocks only), exit-only (no external cylinder), push-button (mechanical or electric), and single cylinder with a removable thumb-turn.
Safety is a concern with double cylinder deadbolts. In a fire, occupants cannot escape through a double-cylinder locked door without the correct key, which can be fatal. This risk can be reduced by locking the deadbolt only when no one is inside, or by leaving the key near the keyhole. Some fire departments recommend placing the key on a low nail or screw near the door, as the cleanest air is at floor level and one may be crawling to exit. Single cylinder deadlocks, with an unlocked interior twist knob, avoid this problem and are common on fire exits. Some fire safety codes prohibit a locked exit entirely.
- type
- Lock mechanism
- common types
- Single cylinder, double cylinder, vertical deadbolt, classroom-function, exit-only, push-button, single cylinder with removable thumb-turn
- inventor of variant
- Samuel Segal (vertical deadbolt)
- key distinction
- Operated only by key or handle, not by spring force
- safety concern
- Double cylinder locks can impede egress during fire
Lore & Background
The deadbolt is a lock mechanism morticed into a wooden door, with a bolt that extends into the door frame. Unlike spring bolt locks, which use a spring to hold the bolt and can be retracted by applying force to the bolt itself, a deadbolt can only be opened by a key or handle. This design makes the door more resistant to forced entry and entry without the correct key. A variant, the vertical deadbolt, was invented by Samuel Segal to resist jimmying, where an intruder uses a crowbar between the door and jamb.
Deadbolts are often used to complement a spring-bolt lock on an entry door. Cylinder-operated deadlocks come in two main types. A single-cylinder deadlock accepts a key on one side and has a twist knob on the other. A double-cylinder lock requires a key on both sides and lacks a twist knob, preventing unwanted unlocking from the interior via a nearby window. However, double-cylinder locks can pose a fire safety hazard, as occupants may be unable to escape without the correct key. Some fire departments recommend placing the key on a nail near the door at floor level, where the cleanest air is during a fire. Single-cylinder deadlocks, with their interior twist knob, do not share this problem and are commonly used on fire exits. Additional deadbolt types include classroom-function locks (thumb-turn only unlocks), exit-only locks (no external cylinder), push-button deadbolts (mechanical or electrical), and single-cylinder locks with a removable thumb-turn.
Reader's Guide
The deadbolt is significant for its enhanced security compared to spring bolt locks, as it cannot be retracted by direct force on the bolt. Its design forces reliance on a key or handle, reducing the risk of unauthorized entry. The double cylinder variant, which requires a key on both sides, prevents unlocking via a broken interior window but introduces a fire safety hazard: occupants may be trapped if the key is not readily available. This has led to fire safety codes restricting such locks on exits. Single cylinder deadbolts, with an interior twist knob, avoid this issue and are common on fire exits. The vertical deadbolt variant specifically counters jimmying. Overall, the deadbolt remains a standard complement to spring bolt locks on building entry doors, balancing security and safety considerations.
Did You Know?
- A deadbolt can only be opened by a key or handle, unlike a spring bolt lock which can be retracted by applying force to the bolt itself.
- Double cylinder deadlocks require a key on both sides and may be banned in some areas due to fire safety regulations.
- The vertical deadbolt, invented by Samuel Segal, resists jimmying with a crowbar between the door and jamb.
- Some fire departments suggest placing the key for a double cylinder deadlock on a nail near the door at floor level, where the cleanest air is during a fire.
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