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For example, if you turn the key for about 45° to lock my house's front door from outside, it can still be opened from inside using the deadbolt knob without a key. But if you turn it for about 90°, then the key is needed even if you would like to open it from inside.

The lock of our front door looks like this one: Door Lock

FYI I'm a native Mandarin speaker and I'm actually looking for the English word for "反锁" in Chinese.

Example sentence:

Hey, buddy, could you please avoid _____ so that I can still open it directly from inside?

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  • Do you have an example sentence?
    – Laurel ♦
    Commented Jan 27, 2018 at 11:12
  • @Laurel Hmm... For instance, how do I say "Hey, buddy, could you please avoid the_word-ing so that I can still open it directly from inside?"
    – Frederick Zhang
    Commented Jan 27, 2018 at 11:15
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    It is known, as both answers below indicate, as either 'double-locking' or 'dead-locking'. In my trade, security, they are both common (in the UK).
    – Nigel J
    Commented Jan 27, 2018 at 14:00
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    One reason this term might not be well-known to modern speakers, at least in the US, is that it's actually illegal (well, against code) to have a house lock that requires a key to get out. That's a relatively recent rule (a couple of decades, maybe; the folks on Home Improvement would have a better idea how recent, and how universal the standard is), meant to prevent people from dying in house fires just inside their front door because they can't find the key. So no new construction or any age of rental will have that kind of lock, and even most older owner-occupied homes have been upgraded.
    – 1006a
    Commented Jan 27, 2018 at 19:32
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    @RonMaupin That's why I included the bit about Home Improvement SE and "how universal" the rule is--I'd guess very few building codes are 100% standard, but I think this one is pretty widespread.
    – 1006a
    Commented Jan 28, 2018 at 4:20

4 Answers 4

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I believe the word you need is the verb deadlock. (Not to be confused by the noun a deadlock, which is a metaphorical sense.) It corresponds to turning the deadbolt in your diagram, as opposed to the latch-bolt.

When you deadlock a door, it is locked, full stop! It cannot be opened without a key (unless there is a deadbolt knob on the inside) . A traditional mortise-lock, such as we have on our front door (as well as a latch-lock) can only ever be opened, on either side, with the key. During the day, whilst we are around we normally keep it on the latch. But at night and when we go out we turn the mortise deadlock.

Older properties such as ours (built 1900) usually have mortise locks. But our rear door, which is on a much newer part of the house, also has one.

It means, if you have such a lock, to remember at night to leave the key close to the door in case you have to get out in a hurry, in the event of fire.

What you have is a lock which combines both a deadbolt and a latch-bolt, both turned with the same key, but which is not effective for the deadbolt until the key is turned 90 degrees.

You need to ask your friend not to deadlock the door, when he goes out.

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  • "It cannot be opened without a key."??? The deadbolt can be unlocked from the inside with the "deadbolt knob" shown in the picture.
    – Laurel ♦
    Commented Jan 27, 2018 at 12:00
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    @Laurel - There's a disconnect between the text and the drawing, because the OP and the answer here indicate that it can't be opened from the inside without a key, but there's no inside key slot shown in the drawing. It makes no sense that the door could only be opened from the outside, where the one key slot seems to be.
    – Jim Mack
    Commented Jan 27, 2018 at 12:14
  • Sorry I wasn't able to find a better drawing. I think you've got what I meant. This type of locks is probably designed for families with kids, so that the kids cannot easily get out of the house when their parents are not at home. But I do think the answer "double-lock" from @edwin-ashworth is also just fine and I'm not sure which is used more commonly. I'd leave the question open for a while to see which one gets more votes :)
    – Frederick Zhang
    Commented Jan 27, 2018 at 12:46
  • @Laurel Sorry I didn't notice the deadbolt knob. In my answer I was talking about traditional UK mortise-locks, which do not usually have internal knobs to turn the deadbolt.
    – WS2
    Commented Jan 27, 2018 at 12:51
  • You're not supposed to need locks down there. / The words used when the handle of a catch on your side of a closed door comes away in your hand, and the barrel won't relocate, are quite different.
    – Edwin Ashworth
    Commented Jan 27, 2018 at 14:22
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I would describe the behavior of locking a door so it can't be opened from the inside as locking someone in.

For example, I would say "Could you please avoid locking me in? I need to be able to open the door from the inside."

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  • 1
    I think this is the least confusing way of asking. If you ask your friend not to "deadlock" or "double lock" the door it may not be clear to him/her what you are asking. You may want to explain exactly how to do this: "Only turn the key 45° or I won't be able to leave in an emergency." (or "if I want to"). If 45° is confusing you could say "only turn the key a quarter turn".
    – Nick Gammon
    Commented Jan 27, 2018 at 23:01
  • You can lock a door so it can't be opened from the inside even when there's nobody inside the room / building. This may be relevant when someone later enters by another door, but can't open the first door.
    – Edwin Ashworth
    Commented Jan 27, 2018 at 23:48
  • But what if for whatever reason, both my friend and I are going out but I still don’t want her/him to do the double-lock/deadlock? I can say “you don’t need to double-lock the door as there’s no one in the house anyway” but how can I express the same thing using “lock somebody in”?
    – Frederick Zhang
    Commented Jan 28, 2018 at 4:55
  • Then it s the analogous "locking me out". While the other two answers are sound, I think this (whether the "locking me in" version given, or the analogous, "locking me out") is probably the most likely to be used in such a request not to do so, since it refers to the problem rather than the mechanism.
    – Jon Hanna
    Commented Jan 28, 2018 at 10:49
  • But I reckon that means using the door chain or some extra locks inside to "prevent me from entering even with a key". dictionary.cambridge.org/dictionary/english/lock-sb-out
    – Frederick Zhang
    Commented Jan 28, 2018 at 12:15
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At least in British usage, the verb and corresponding noun most usually used is probably double lock (though the term is admittedly fairly rare):

double lock in British

noun

  1. a spring lock that can also serve as a deadbolt by an extra turn of the key

double-lock in British

verb (transitive)

to lock by means of a double lock, or by more than one lock

We double-lock our doors and clutch comforting cups of tea.

{Collins}

M-W licenses the usage in 'AmE':

Definition of double-lock : to lock with two bolts or by two turns of the key : fasten doubly

'Deadlock' appears to be a hypernym:

Double lock: A type of spring lock which may be used as a deadlock by an extra turn of the key.

{ODO}

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  • I think you are right. Although I am familiar with both 'dead-lock' and 'double-lock' I meet 'double-lock' more often in the UK.
    – Nigel J
    Commented Jan 27, 2018 at 14:03
  • I can "double-lock" my front door simply by pushing the handle up (which extends several internal locking bars). But although the door is then held securely on all sides (rather than just the hasp by the handle), it can still be opened again by simply pressing the handle down (which I can't do if the key has been used).
    – FumbleFingers
    Commented Jan 27, 2018 at 20:04
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    @FumbleFingers that doesn't fit with the definition of double-locking I'm used to: If you shut the door and do nothing else, it latches. With a pad handle you can't then open it from the outside. Then some action taken to secure it is locking and a second action double-locking (Southern England FWIW)
    – Chris H
    Commented Jan 27, 2018 at 22:00
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The main term for this is "deadlocking", but locking someone in a room or building that can only be locked from the outside is technically imprisonment, especially if it's against the persons will.

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