Dead bolt

Types of Deadbolts
– Single cylinder deadlock: accepts a key on one side and is operated by a twist knob on the other side
– Double cylinder deadlock: accepts a key on both sides and does not have a twist knob, preventing unwanted unlocking from the inside
– Lockable knob: requires a key on one side and can be operated by a twist knob on the other side, unless a button has been pressed
– Vertical deadbolt: resists jimmying by inserting a crowbar between the door and the jamb
– Other types of deadbolts: classroom-function, exit-only function, push-button deadbolt, single cylinder with removable thumb-turn

Safety Concerns
– Double cylinder design raises a safety issue in fires, as occupants may be prevented from escaping without the correct key
– 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 placing the key on a small nail or screw near the door at floor level for easy access in a crawling position
– Single cylinder deadlocks do not pose the same safety issue and are commonly used on fire exits
– Some areas have fire safety codes that prohibit locked exits

Related Topics
Door security
– Lock bumping

References
– ‘What is a Deadlock? Everything you need to know | Locksmith Direct.’
– ‘How to Repair a Doorknob – Old House Journal Magazine.’
– Abloy. Lockable Thumbturn H2X Deadbolts.
– Kennedy, Les. ‘Deadlocked doors seen as fatal in house fire.’ The Sydney Morning Herald.
– Hardware requirements for access and egress (PDF). Canada government. Archived from the original (PDF) on 27 March 2014. Retrieved 12 June 2014.Sources: https://en.wikipedia.org/wiki/Dead_bolt