My front door has a mailbox slot which makes it really easy to operate the inside door handle from outside with a long object. One solution I'm considering would be a mailbox secured to the door over the mailbox slot. Another option I'm considering (possibly both) is always locking the door from the inside. However, for fire safety reasons I would need a thumbturn, which would lead to the same issues. Hence I was wondering if there is such a thing as a security thumbturn that's a bit harder to open with burglar's tools?

Of course everything can be opened with sufficiently advanced tools, but I was hoping there were thumbturns that were designed to at least be slightly trickier to open than the default design, e.g. by requiring some finger dexterity that burglar's tools are unlikely to have. Is there such a thing and does it have a generic name? "Security thumbturn" isn't giving me a lot of results.

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    "Childproof" tends to be a term to look for when trying to thwart basic grasping tools. Commented Oct 5, 2021 at 12:40

4 Answers 4


Rhetorical questions that bring amazement:

  1. Can an adult actually get his arm through the mail slot up to the elbow to reach the doorknob without getting his arm stuck? If so, that's a massive fail in the mail slot design and someone should have his knuckles smacked with a ruler for that!

  2. Did someone actually install (or was it purchased that way) the mail slot that close to the doorknob? If so, that's a massive fail in the mail slot installation and someone should have his knuckles smacked with a ruler for that!

Suggested Answer:

  1. Have you considered a simple guard installed above the slot to, effectively, make the door "thicker" in that spot, requiring more arm through the slot before the elbow can bend upward to reach for the handle? It might look something like this lovely bit of ASCII art. (Looking at the narrow edge of the door)
Inside         Outside

      |   |    This is the door
   ---|---|    This is the top of the slot with a guard above it
      |   |    This is the slot
      |---|    This is the bottom of the slot
      |   |    The rest of the door

Make the guard bit (--- in the drawing), extend toward the inside as much as necessary. A would-be thief would have to get his arm far enough through the slot to get his elbow past the inside edge of the guard before bending it up to reach for the doorknob. This means that the bicep/upper arm has to fit through the mail slot. Most adults, with arms long enough to reach from the mail slot to the knob, would have arms too big to fit that far through the slot.

Of course, you could hang a basket for the mail from the guard so that the mail moves with the door, or even a full-on mail box there, too. Do remember, the basket/box needs to be tall enough that someone can't reach through the slot to steal the mail - that'd be almost as bad! (And is probably why mail is simply allowed to fall to the floor).

Alternate suggested answer:

In response to the desire to make it difficult to turn the deadbolt (thumb turn) with a coat hanger or other object stuck through the mail slot, I'd suggest a "child safety door knob cover" that would be placed over the thumb turn. Something along the lines of this item (image sourced from Amazon)

Child safety door knob cover

While ugly, any such cover, would, if sized correctly make it nearly impossible to operate the latch with a simple tool being wielded blindly through the mail slot, yet allow for easy operation of the deadbolt by nearly anyone (except, of course, for a small child, against whom it's designed to protect in the first place) if/when it comes time for an emergency egress.

These are usually soft rubber that are easily squeezed to enable anyone from the age of 6 (or so) on up to grab, squeeze, and turn the knob underneath, while preventing simple operation by something unable to provide the necessary leverage to do the squeezing.

  • 1) An adult couldn't fit through the slot, a child could maybe do it. But that's irrelevant as you can open the door with a simple coat hanger. 2) The mail slot is that close to the door knob yes. I have no idea who installed it that way. Commented Oct 5, 2021 at 13:24
  • The mail slot is to the side of the handle, not below the handle. But yes, I have considered installing a guard, but decided against it because it would be ugly. Commented Oct 5, 2021 at 13:25
  • And that, @FrederikVds is the failing with lever-style handles. (Yes, I understand they have other advantages.)
    – FreeMan
    Commented Oct 5, 2021 at 13:26
  • The handle is basically irrelevant, it only operates one tiny latch bolt which is way too easy to shim anyway. The only way to engage the dead bolts is with the lock itself. That's why I want a thumbturn to operate those from the inside to make the door easy to lock properly and not as trivial to open through the mailbox slot as the handle. Commented Oct 5, 2021 at 13:30
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    Note update, @FrederikVds
    – FreeMan
    Commented Oct 5, 2021 at 13:38

You, without realizing it, kind of answered your own question about the "security thumbturn" not giving a lot of results, FIRE SAFETY. Any type of thumb turn that would be "tricky" to turn could be a real problem for children and elderly persons to operate in an emergency. We have fire inspectors routinely give home safety lectures and this is one subject that always comes up.

Your best bet would be to secure your mail box or disable it and install a mail box somewhere else. I'm actually surprised the Post Office hasn't approached you about this because they don't like to get out of their trucks now.

  • Not just children and the elderly, but fully capable adults in their mid-20s in full panic mode are often incapable of performing the most basic functions that even a low functioning adult would do without second thought when there's no pressure on.
    – FreeMan
    Commented Oct 5, 2021 at 12:47
  • Perfect is the enemy of good. At this point, our door is often locked completely with no way to open it if you don't have a key with you. I'm looking for a solution that's reasonably secure against burglary and reasonably safe in case of fire. Not sure what the post office thing is supposed to mean. I obviously can't put a mailbox in the middle of the street where a postman could access it without leaving his car. I've also never seen a postman using a car in the first place. They usually ride a bicycle. Commented Oct 5, 2021 at 13:21
  • In the US, big city mailmen may walk their rounds, but even in a city of 1 million, they'll drive. In my rural town of 750, we don't even get to have our mailbox in front of our house - they're in groups at the end of the road so the mailman drives up one road and delivers mail for everyone on the cross street. We have to walk to the end of the road to get the mail from the mailbox.
    – FreeMan
    Commented Oct 5, 2021 at 13:30
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    @FrederikVds The post office thing was meant to say that in many areas they have required mail boxes to be relocated to front property lines so they don't have to walk so far or get to stay in their little trucks. Then you could disable your mail slot in the door and get a regular thumb turn for a lock.
    – JACK
    Commented Oct 5, 2021 at 16:14

The usual recommendation (speaking as a locksmith) is that, if you are really concerned about this, you should consider a double-cylinder lock with a "thumbturn key" kept in the inside lock whenever anyone is in the house, or at the very least hung on the wall adjacent to the door, at a height kids can reach, perhaps with a chain just long enough to reach the lock so you can guarantee it won't walk off but it will still be available when needed.

In fact, some companies have make this into a product -- a thumbturn body that attaches to a key, with the key modified so it latches into the lock when inserted and requires an "ejection tool" to remove it. That makes it look more like an ordinary thumbturn, prevents it from walking off, but still permits removing it when necessary. I don't know if anything along these lines is currently available on the market; I haven't kept up with the trade in the past decade or two... but an active locksmith should be able to research it for you.


Stumbed here for the same reason, worse we have a cat flap. Dont want a key on the inside as its fire risk if we deadbolt at night and cant leave without a key, and if leaving key in lock might aswell have a thumbturn. Anyway, I have explored letter box shrouds, but there is no security available for catflaps. But discovered this: https://tradelocks.co.uk/kinetica-3-star-kitemarked-child-safe-thumb-turn-euro-cylinder-locks.html It is a thumbturn that requires a double motion to turn. Marketed as a childsafe feature, their documentation also states it prevents against common attacks, which i can see as the leverage to push the thubturn is going to be difficult with a coat hanger! Its also a decent lock outright. Heres it being picked: https://www.youtube.com/watch?v=C0CZhBjTlhU&ab_channel=LockNoob

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    Hi Ryan, having just links for answers is not ideal. You could improve it by adding pictures of them. Commented Oct 30, 2023 at 10:12
  • True, @RohitGupta, but he does describe what the product does which, at least, means this isn't a "link-only" answer. ;)
    – FreeMan
    Commented Oct 30, 2023 at 12:28

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