Suppose I have an office door that has decorative glass on one side of the door. The risk to me is that the window pane could be shattered and a gloved hand can manually unlock and open the door from the inside.

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  • What terminology and type of lock is appropriate for securing this type of door (as much as possible) without reinforcing the frame?

(I'm not looking for shopping examples for door locks, but am interested in terminology and criteria I should use to independently research these)


2 Answers 2


The window pane in your example photograph is wide enough to allow entry for more than a gloved hand; an entire intruder body could fit in the hole, should the pane be wholly removed. At that point, the lock becomes irrelevant.

Moreover, for safety reasons, chances are that the unlock mechanism from the inside must remain operable without a key; otherwise, someone could be trapped and unable to exit in a swift manner should a fire occur in the room. Under these conditions, there is probably no lock which will ensure security (or even simple improve security by a non-negligible amount) as long as there is a breakable window large enough to allow the "gloved hand". Also, note that an intruder who is ready to break a window could also have a crowbar; a wooden frame won't last long.

Therefore, I suggest that you do not look for a lock but for some way to reinforce the window itself, or for a deterrent (motion detectors and alarm in the office; armed guard and/or fierce dog on the inside or on the outside; additional protection layers, e.g. a safe or strongbox, for important assets in the office; and so on).

  • or indeed use the principle of layered security and provide better security for the things that lie behind this door. i.e. assume that the door will always be a threat and apply security to the things inside. Aug 14, 2013 at 7:53

Aside from the excellent points noted by Tom Leek, to answer your question exactly: You want a double cylinder deadbolt, which is one with keyholes on both sides, and no thumb-turns at all.

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This means that even if someone were to smash the glass, they would be unable to turn the lock cylinder without a key. This also means that if the locked door is the only exit from a room/building, and the building catches on fire, and the occupants don't have a key, they will perish.

Which is probably why double cylinder deadbolts are infrequently seen in the wild; in some jurisdictions they are forbidden by building codes/fire safety regulations.

  • 2
    Solution: place the key in emergency key box, close to the door, but far enough that a potential intruder cannot reach it from outside by hand.
    – Trang Oul
    Feb 3, 2016 at 10:51

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