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Berlin Key (wikipedia.org)
446 points by woozyolliew 24 days ago | hide | past | web | favorite | 147 comments

The English description on that page doesn’t make it easy to understand what this key does.

”Its name comes from the fact that it has two key blades (the part which activates the bolt) at each end of the key, rather than the usual single blade”

How does that lead to the name “Berlin key” or either of the German names? I would guess “Berlin key” comes from the fact that it predominantly is used in Berlin.

”After unlocking the lock, the key must be pushed all the way through the lock and retrieved on the other side of the door after it has been closed and locked again”

I think the main features are:

- the key cannot be removed when the lock is open.

- you can remove the key from the other side of the door from which it was inserted.

It seems you can lock the door from the side it was unlocked from, and remove the key from that side, too. You only have to push it all the way through if you want the door closed and locked with you and the key on the other side of the door.

I also think you can close the lock and remove your key when the door is open.

The Berlin key ("Berliner Schlüssel") was mostly used in tenements with multiple backyard houses with a common front gate that should be closed at certain times. These kind of arrangements were mostly used in Berlin, hence the name.

The other German names for the key describe different aspects of it: "Durchsteckschlüssel" translates to "push-through-key" and "Doppelschlüssel" translates to "double-key".

If you are more curious about the thing, there is a book by philosopher Bruno Latour on the Berlin Key where he describes the thing with the sociological situation that lead to it if I remember correctly (was a few years ago when I read it).

Edit: The basic idea is that in this kind of multi-party environment they wanted to make sure the door is always locked in the evening (when people return). To unlock the door you have to push the key through. Once you are inside you can get the key back, but only if you lock the door behind you. So once the door is locked, it stays locked, unless someone from the inside leaves it open on purpose. This way people cannot "forget" to leave it open.

Please contribute to the Wikipedia page, you seem to have some better information than is there currently.

It would be reverted immediately. Requires external sourcing.

The other names are already on the German wikipedia page: https://de.wikipedia.org/wiki/Durchsteckschl%C3%BCssel

Sounds like a very German approach to following rules and influencing behaviour.

May I ask why you read a book on it? Just interested in locks/security or lock picking?

I’ve found reading general interest books are a great source of inspiration regardless of your speciality. So I like picking up random topics. For ex: a book on ants which had utility in simple autonomous network design.

The building I live in in Berlin, 1910-ish construction with two more wings in the courtyard, everything accessible through the front gate - it has the same principle implemented with a timer and a button. I thought it's a bit odd, but made some sense after a while.

During the day, the front gate can be opened from the outside with just pushing a button that unlocks the door. At night (from 20 or 21 or so), the button stops working, you need the key. It can be opened at any time from the inside without keys. So it's more or less implementing the same protocol, but electro-mechanically, so there is no need for the trick with pulling the key inward.

I might be misunderstanding the old school original situation, but your modern setup does not enforce/encourage that the door is closed. Even an automatic closing mechanism could be blocked by something.

With the Berlin key if you want to get your key (ostensibly you do and certainly don't want someone else to take it) you have to close the door. Of course you can still leave it propped open but unlike in your modern setup you actually have some stake in making sure it is closed.

So here a video is worth a million words :)


Edit: I read the first paragraph twice and then to confirm my understanding I turned to YouTube.

Something vintage about video.

They showed the key on video facepalm

I get the sentiment, but to mount this attack you’d:

* have to clone the key from fairly dark and jittery cell footage

* have to identify the location in a city of four+ million people

Once you did that you’d be able to access a commons area of a hotel?

I’m not convinced the risk is all that great :)

It also looks like a lever lock. Old lever locks tend to be pretty easy to defeat by means easier than cloning the key from an image.

> Its name comes from the fact that it has two key blades

Until recently, this sentence used to be “Its particularity comes from the fact …”:


I agree it is really hard to parse. I think you're almost right. I'm pretty sure it's like this:

1. You can only remove the key if it is locked. 2. You can't lock it unless the door is closed.

That ensures that when you have the key then the door must be locked and closed.

The think about pushing the key through they door is just because otherwise you have no way to start inside the room, unlock and open the door, and then lock it behind you. Remember while the door is unlocked you can't remove the key. So if you just go outside and shut the door the key is now inside... and the only solution is to pull (or push) the key through to the door to the outside. Then you can lock the door and remove the key.

Video showing how it is used, really neat!


Something that isn't entirely clear to me from the video. Do you have to push it from the inside to retrieve it outside? Because that would be super annoying.

How so? The only time you use the lock, you are leaving or entering, and the key forces you to lock the door in order to retrieve the key on the other side.

It would be be better if once I unlock it, the key gets pushed by some mechanical spring, instead of me manually having to push it from the unlocking side to get it on the locking side.

It seems that you can accidentally, or not, lock the door without fully closing it, thus leaving it essentially unlocked, so the key isn’t quite fool-proof.

Some have a lever on the edge of the door preventing the key turning if the door isn't closed

>so the key isn’t quite fool-proof

Yes, it's from another era, when the consumer was not expected to be a fool...

That's one way to describe problematic design. In other words, the key doesn't fulfill its intended purpose considering (as the comment you replied to noted) one can do this either accidentally or not which can have little to do with being a fool.

This key goes to great lengths to make sure the user doesn't lock themselves out. It seems specially designed for 'fools'.

I'm surprised some houses still use this. As it's impossible to leave the building without a key in case of a fire.

I suspect it may even be illegal today.

As an American living in Switzerland one thing that has consistently surprised me is the difference in fire safety rules: not having any smoke alarm or fire extinguishers in homes is common, and it's also common to be able to lock people inside rooms/apartments/buildings so that they can't leave without having a key. It's possible to lock someone in my apartment even if they have the key if the door is locked with the key left in on the other side.

In the US if I checked out a rental home as a possible place to live and it had any one room where you could lock someone in and they would be trapped I'd wonder what weird shit happened there.

You are much more likely to die in a fire in USA, so it makes sense for Americans to take more measurements to prevent it. But in for example Switzerland fires is not a big thing so there is no need to have any laws against it.


I'm also guessing german europe (swiss, austria, germany) lives in an earthquake free zone, so they can make stone buildings without much consideration for earthquakes while most of the US population has to think about earthquakes and/or hurricanes, so housing is more likely to go towards flexible and flammable wood.

Actually, it's mostly a cost thing. US code allows very inexpensive building materials and practices relative to Europe.

I suspect that is a result of different cultural expectations related to who should be able to afford to own their own home - even if the homes don't last very long.

The choice of wood for residential housing is based on cost. Trees are plentiful in the U.S., so wood construction is the cheapest option. In countries without lots of trees, they’ll use concrete, stone, or something else.

Germany has plenty of wood, and ~300 years ago the majority of buildings were made from wood, with straw and clay as filler material, and straw roofs.

From my understanding the switch to stone was mostly for fire resistance. City walls lead to very dense cities where fire could spread rapidly. Stone walls with clay tile roofs make it much harder for any fire to spread within a building and to other buildings.

Today we would have the fire fighting techniques and more fire resistant wood panels, but old habits die hard (and we are used to buildings standing for hundreeds of years)

In a house fire you'll usually be killed by your burning synthetic furnishings before the burning structure gets much of a chance.

Based on this data, the fire death rate in the US is 1.16 per 100k pop. and the rate in Switzerland is 0.28 per 100k pop. Percentage wise, that's a big difference, but that's only because both of these numbers are extremely small. I don't think it's really accurate to say you're much more likely to die in a fire in the USA; it's extremely rare in both countries.

1.16/0.28 is a big difference.

If Switzerland had the US rate, ~75 more people would die every year.

If the US had the Swiss rate, ~2800 people would live to see another year.

I know the US (330 mil. pop.) is a much larger country than Switzerland (8 mil. pop.). You also could have said: "The cost of improving the Swiss housing and infrastructure to reduce the mortality rate due to fire would be a miniscule fraction of what it would be in the US". You have to normalize to look at these things, and you also have to look at the bigger picture, or you could totally mislead yourself.

Put in normalized terms,

- 0.00028% of the Swiss pop. dies from fire annually

- 0.00116% of the US pop. dies from fire annually

- 0.001% of the US pop. dies from drowning annually

- 0.001% of the US pop. dies from exposure to mechanical force annually

- 0.006% of the US pop. dies from gunshot annually

- 0.01% of the US pop. dies from falling annually

- 0.015% of the US pop. dies from road injuries annually

- 0.03% of the US pop. dies from respiratory illness annually

Here's [0] a visualization I made of causes of mortality a few years back. Play around with this a little bit; it's pretty interesting looking at actual mortality rates.

[0] http://bl.ocks.org/MattTriano/raw/154e9c142504d61985e2b65287...

An extra 2800 people out of a population of 380 million? Statistically meaningless.

The victim death count from 9/11 was 2,977, and that appeared to have at least some effect on the American psyche

The deaths didn't. The news coverage of the deaths did.

Don't know about Switzerland, but as an European living in the US, I think the American fire safety rules are what they are mainly because most houses here are basically matchstick houses built from prefab low quality wood which would get devoured by flames in minutes. And the fire-resistant building materials are super toxic when they actually burn. So fire is a very big deal...

Anecdotal, we had a fire in my building because the wrong type of lightbulbs were installed in the hallways and because of their size, they were too close to the drywall which in turn caught fire. So.. yeah. Matchstick.

I stayed in a house in Germany in which the walls were filled with dried-straw for insulation. It was several hundred years old. There was a no-smoking rule.

I have a similar anecdote. The walls of the main building at my university were full of hay and paraffin wax. This is in the UK. We were very conscious of fire safety there...

> There was a no-smoking rule.

Which to be honest says not a lot about anything, because this isn't that unusual in Central Europe.

Also: a lot of the old wooden houses are far better in terms of fire resistance than you'd suspect on first glance, wood often outperforms concrete and steel when it comes to structural integrity in a fire.

I don't know about the straw thing, I only know it mixed with clay.

The no-smoking bit was me being a bit, ah, dry. Sorry it didn't come across better.

The home in question belonged to the extended family of my host family while I was an exchange student. I went with them to a maintenance day and did wallpaper. I got a very close look at the walls, not to mention the repeated lectures on what a firetrap it was.

Trust me, it was.

For about the last 20 years of my life as an American, 99.9% of all buildings I enter have a no-smoking rule. The only exceptions have been bars in kind of backwards places that I've had to go on business, like Jacksonville, FL.

> Don't know about Switzerland, but as an European living in the US, I think the American fire safety rules are what they are mainly because most houses here are basically matchstick houses built from prefab low quality wood which would get devoured by flames in minutes. And the fire-resistant building materials are super toxic when they actually burn.

Also US electric plugs are inherent fire hazards, much more so than anything you find in europe.

It’s probably more to do with the age of the buildings. Generally you don’t need to update the safety level to today’s standars unless you do some major changes.

It may or may not be the case that US houses catch fire more often, but fire is always a very big deal if it does happen and then you really don’t want to be locked inside the ‘fire-proof’ house.

> prefab low quality wood

Excuse me? What exactly is "low quality wood"?

What are you claiming determines "wood quality"? And are you insinuating that "high" quality wood somehow... burns more slowly or something? All of this is new to me...

Also the vast majority of US homes are not prefab at all, not sure what that has to do with anything. And I'm not aware of a correlation between prefab construction techniques and fire hazards.

Now it's absolutely true that different parts of the world use different materials -- cinder blocks vs. wood vs. stone -- but that has much more to do with climate, available materials, and century of construction, rather than "quality".

Wood generally falls into two categories: hardwood and softwood. Hardwoods like oak are more dense, harder to light, and take longer to grow, so they are more expensive. Softwoods like pine are less dense, easier to light, and grow faster, so they are cheaper. Within each category there are additional ranges of cost and quality.

New homes in America tend to be wood-framed. Cheap materials are popular in American home construction.

https://en.wikipedia.org/wiki/Hardwood https://en.wikipedia.org/wiki/Softwood

Thank you, you beat me to it.

I would add this article https://www.bloomberg.com/news/features/2019-02-13/why-ameri... which explains my matchstick metaphor

> Building codes evolved, too, as insurers and fire-safety-equipment manufacturers pushed for scientific, “performance-based” codes that emphasized lab-determined fire-resistance ratings over specific materials and incorporated new technologies such as the automated fire sprinkler.

> Stick construction allows builders to use cheaper casual labor rather than often-unionized skilled tradespeople. And it makes life easier for electricians, plumbers, and the like because it leaves open spaces through which wires, pipes, and ducts can run. Still, there’s a reason why stick wasn’t the default for big apartment buildings until recently, and why these buildings are limited in height: Sticks burn.

> Now it's absolutely true that different parts of the world use different materials -- cinder blocks vs. wood vs. stone -- but that has much more to do with climate, available materials, and century of construction, rather than "quality".

Another reason you missed is money. Ticky tacky is cheap and ubiquitous in your average dwelling in America.

I grew up in Austria and live in Germany (so two neighbouring countries to Switzerland) and here it is mandatory to have at least smoke alarms. Fire extinguishers are mostly only needed for public buildings and server rooms and such. Germans especially take their "Brandschutz" very seriously especially regarding emergency exits etc.

However in the end you are responsible for your own safety. If you are in a room with a lock, make sure you don't lock yourself in. Locking people in is a bad idea regardless of situation (and I am pretty sure it is illegal to do so against their will).

> Locking people in is a bad idea regardless of situation (and I am pretty sure it is illegal to do so against their will)

As an American I still find it weird that it is even possible to lock someone in: anyone I've asked has had stories about young kids locking themselves or their parents in or out of a room with no easy way to fix the situation (resulting in things like balcony jumping). I don't see the benefit in designing things that way.

You should also take care not to light your house or person on fire, which is a bad idea and probably also illegal (regardless of will).

I'm currently living in an apartment in Switzerland where the house and the whole street is a UNESCO World Heritage. Due to the building regulations that accompanies, lots of wood is still used. Like for example the whole attic is made of wood.

Because of that we can call the firefighters at not cost, even false alarms are not penalized. But no mandatory smoke alarms or fire extinguishers even though this building still has a working old time furnace for heating. Go figure.

Maybe they expect the Swiss neighbor watch to raise an alarm more accurately than a smoke detector would. Old Swiss people are always suspiciously watching over their neighbors.

I guess it could still depend on country, but in EU smoke alarms are mandatory.

No one checks it for individuals though.

Are they checked for individuals in the US? The only time this would be verified is after construction which is when they'll also be checked in the EU.

Fire control rules are somewhat different between the US and Europe. In Germany, such a system would be fine. Depending on the door even encouraged.

A large part of German Fire Code is to prevent the spread of the fire and contain it in the rooms where it started for as long as feasible. The lowest rating a fire location can have is E30, meaning the fire takes 30 minutes to "break out" and spread further. The building owners likely also benefit from grandfathering (ie, special building fire code, which depends on federal state in germany).

It also depends on the fire load, ie, how much flammable material the house contains. A concrete or stone house that contains only flammable material as part of furniture isn't a huge fire load and you don't need heavy doors to prevent fire from spreading out of a single flat, a normal door will likely already prevent spread.

> As it's impossible to leave the building without a key in case of a fire.

Isn't that the case for most doors that lock? You can't leave through my (brand new, to-code) front door from inside without a key to unlock it first.

It wouldn't be secure if you could open it without a key - isn't that the whole point of a lock with a key?

> You can't leave through my (brand new, to-code) front door from inside without a key to unlock it first.

I'm sure I'm just ignorant, but it sounds like your lock is on backward. Every front door I've ever seen can be unlocked from the inside without a key.

Example: https://www.lowes.com/pd/Schlage-Deadbolt-Satin-Brass-Single...

Could you link to a lock that's similar to what you're talking about? I'd feel very uncomfortable entering a house where I couldn't leave without a key.

This is what a lock in Germany and most of Europe looks like: https://proxy.duckduckgo.com/iu/?u=http%3A%2F%2Fmax-attachme...

It's the same from both sides (except for the screws, you can only unscrew it from the inside). Both the inside and the outside have a keyhole, and while a key is in one side you can't put a key in all the way from the other side (this way you can lock from the inside, leave the key in, and even someone with the key can't get in).

Normally people don't lock the door while they are inside (maybe at night), on doors facing outside the door handle can't be turned from the outside and you have to use the key to get inside even when the door isn't locked.

You can replace the lock with one of these: https://5.imimg.com/data5/EI/SP/MY-3690463/hardwyn-hcl-301-2...

I don't think I ever saw these used in a residential setting. Commercial buildings are a different story.

I have locks like this in my home. I got a new front door and locks when i moved in [1], and the locksmith offered me the option of these (it's called a thumbturn lock here), which of course i took, because it means you don't need a key to hand to open to door to let someone in, or to escape a fire.

[1] because the previous owner's tenants had broken the door down at some point, and he had replaced it with an internal door, in which for some reason he had installed the lock upside-down

I've not seen them in Germany for example, but the cylinders were standard, so it's an easy swap (you can keep the old lock and swap it back if you leave). Keeps you from being locked out, for sure.

In Sweden I only recalled having seen internal keyholes on older installations, newer homes have a turn on the inside. Haven't lived there in years tho so only going off of vague memories.





Most homes where I grew up in Europe had two locks, one which you could open without a key from inside and one which requires it from both sides. Not sure why it was like that, but it feels normal to me.

Around here (Finland) basically all homes have locks that open without a key from the inside, plus optionally an extra lock that needs a key on both sides, for those who desire more security. I presume those extra locks are more common on house doors than apartment doors.

Yeah that's the same as the UK-setup as the parent described.

99% of the time most people use the latch, which would be a Yale lock in the UK, or a Abloy in Finland. You'd usually use the extra-lock if you went on holiday, or something similar. Most of the time it would be unused.

Here's an example of my deadbolt that's keyed on both sides: https://i.imgur.com/xXzWS7j.png

Those are peodominately used in situations where someone could reach in (via a broken window or space between bars) and simply unlock it. A solid door should not have this type of lock in the US.

I think it could be a US / Europe thing. In the UK (where I'm originally from) I think almost all door locks I've seen require a key to unlock from the inside, but in the US (where I've lived for 7 years) I don't think I've ever seen one - they deadbolt usually has something that you can unlock by hand without a key from the side (and not even an option to lock it from the side with a key).

I'm also from the UK but I left more than 30 years ago. I feel nervous every time I visit my family in the UK because now they all have locks that require a key on the inside and frequently the key is misplaced.

I understand the reason for it but I wish a better solution could be found.

> A solid door should not have this type of lock in the US.

Why not? Someone smashes a window, crawls through it, walks around to unlock the main door, through which the burglars unload your stuff. It’s a lot harder to move things through windows.

I think I'd rather optimize for fire safety than for the possibility that I might lose more stuff if someone breaks in and can more easily unlock my door from the inside.

What about the hinges? If the burglars are inside they can take the door off the hinges instead of unlocking it.

It's not visible in the photograph, but this door has a glass window in the center of it.

It's only less secure if there's something easy to break close enough to the door that a person could break it, reach through, and unlock the door. That's only really relevant if there are no windows anywhere else at ground level that a burglar could easily break and climb through.

Interestingly, the door locks commonly used in the US are much less secure in general than those typically seen in Europe. The average US household deadbolt can be opened with fast lockpicking techniques (raking, zipping) while European ones usually can't. That may be a surprise given the relatively high crime rate of the US.

One crime that isn't as high in the US as most European countries, however is burglary of an occupied residence. It seems the increased risk to the burglar's life may have some deterrent effect.

What country do you live in? In the US, almost every door I’ve ever seen can be unlocked from the inside (but not the outside) without a key.

In recent years, American apartments I've lived in have made it impossible to lock the front door from the outside without a key so you can't lock yourself out, thereby eliminating the need to call the landlord or manager over incidents like that.

They have a knob that doesn't have a locking mechanism at all and a deadbolt that locks from the inside without a key, but cannot be locked without a key if you leave.

I've never seen that outside the US. Keyholes both sides of the door, everywhere. When it's closed, you need a key or you don't get out.

Some places have euro-profile locks with thumb turns for the inside.

I think in some English rental properties these are compulsory. (Or Yale latches).


Well, TIL. Never realized this was a US-specific thing.

It's definitely not US specific. Here in Denmark it's standard that the front door opens from the inside without a key. Same goes for at least Luxembourg and Germany as far as I know.

Germany checking in: all the front doors I know are two stage: first stage closes just by falling into the lock and and opens keyless from the inside, second stage requires key action for both closing and opening, on both sides.

Same for Poland.

Add Finland to the list. Pretty much all of Central and Northern Europe I believe. I don't think I've ever seen a residential exterior door that needs a key to open from the inside.

It's not. Same in Australia, I've never seen a house here you need a key to get out of.

If you lock a security / screen door from the outside, you generally cannot open it from the inside without a key

I don't think it's US-specific, as I have seen it work the "US" way abundantly when traveling.

But having it not work this way is very unusual in the states, while common to not exactly rare in some other places.

Same thing in Russia

The UK. What stops someone breaking glass or a panel and reaching through and unlocking to get in quickly if you can open without a key?

You either have strong or no glass on or near your front door.

I have never seen an exit door in Canada, or the United States, that could not be opened from the inside. I'm reasonably confident that is super illegal in those countries.

> What stops someone breaking glass or a panel and reaching through and unlocking to get in quickly if you can open without a key?

I suppose this can be avoided by not having any windows close enough to your doorknob that you could reach the lock from them. But people could just break a window and climb through into your house, anyway.

I think doors that can't be opened from the inside are serious possibly criminal safety violation everywhere in the United States.

> > As it's impossible to leave the building without a key in case of a fire.

> Isn't that the case for most doors that lock? You can't leave through my (brand new, to-code) front door from inside without a key to unlock it first.

Do you live in the US by chance? In my jurisdiction double keyed deadbolts for example are not up to code for residential use, and for those applications the deadbolt must be keyless on the egress side.

Logically, this seems sound as you don't want to be scrambling for keys if your house is on fire.

> You can't leave through my (brand new, to-code) front door from inside without a key

Just to clarify, after you lock your front door with the key, it’s impossible to unlock the door from the inside without a physical key?

The vast majority of locks have a physical unlocking mechanism on one side (one side is unprotected, usually the inside)

> The vast majority of locks have a physical unlocking mechanism on one side

Not where I live. Sure the lock that you use to stop it blowing open in the wind (1) when you are at home has a latch on the inside (making it easy to open door to visitors etc), but you also have the real lock that you use when you leave the house require keys from either side (2).

I think most home insurance in the UK would either not insure you or your premiums would be super-high if you only had the latch and not a proper secure lock.

Random image from the internet showing typical UK front door locks - latch at the top (openable from inside without key), proper secure mortice lock at the bottom (key needed from both sides): https://i.pinimg.com/originals/1b/a1/63/1ba1634b8b6b9c5135b6... or https://i.pinimg.com/originals/a1/7b/77/a17b77bf1ad7a909a0bd... - in the second picture if it just had the latch it would be absurdly easy to break into: just break the glass and open the latch!

1 - https://www.screwfix.com/c/security-ironmongery/night-latche...

2- https://www.screwfix.com/c/security-ironmongery/door-locks-b...

As long as you don’t have easily breakable glass within reaching distance of the unlocking mechanism, why is a lock that can be unlocked from inside less secure?

I think the problem is not that it can be opened from the inside but more that the ones that just have a lever to flick on the inside are usually yale style locks that are easy to bump or pick, or break a window and reach, or put something through the letter box to reach.

The mortice locks are harder to pick and are usually substantially sturdier in construction. In the UK at least, the mortice lock is physically inside the door structure (1) whereas the latches that don't need keys are attached on the door (2).

We recently had a break-in in the block of apartments where I live where the latch attached on the door was broken off by people forcing a door. If there had been a mortice lock, they'd have to break the door frame or the door itself, rather than just bust the weak latch lock off the back of the door (in this case the door opened outwards, so they just pulled on the door handle whilst bracing a leg against thethe wall and the latch came right off the back of the door)

1 - https://www.buildingsheriff.com/mortice-lock-costs_files/sta... 2 - https://www.diydoctor.org.uk/images/nightlatch.jpg

Because breaking through one small panel on a door and then reaching through and turning the lock is a lot easier than having to break away the entire door so you can get your body through.

> The vast majority of locks have a physical unlocking mechanism on one side (one side is unprotected, usually the inside)

Maybe where you live. I’ve never seen a lock like that except in a hotel.

Coming originally from the UK I was surprised about how relaxed fire and safely regulations are in rented accommodation is in Germany.

This is super clever, but I bet some of its potential applications conflict with egress safety requirements/laws.

(If a door is part of an exit route, you probably can't require a key to open it.)

Makes me wonder: how are prisons handling fire safety?

Cynically, probably through legal exceptions and active 24/7 staffing that can double check fire alarms.

Certainly the meeting point is in the central yard, and there are probably hundreds of false alarms for fun.

Good point, but I doubt those rules existed anywhere in 1912 when this key was invented.

It seems like you could have a similar system which also has some type of internal lever to release the lock although I assume this wasn't part of the original design.

Not really. When you can open it from the inside without using a key, you can then also leave it open without that key being inserted into the door, if necessary by propping up something to the door to prevent it from closing itself (from what I understand, you could even use the door’s bolt for that; if you close the bolt while the door is open, you can remove your key, and the door can’t be closed without a key)

I doubt that’s theoretical. Kids playing in the garden and on the street could easily use that ploy.

That would defeat the purpose of the key design, which is to ensure that you lock the door behind you.

It's kind of confusing but easier to understand when you consider the primary goal which is to force people to lock the door.

This is achieved by only allowing the key to be inserted or removed when it's in the locked position. The push through is to allow them to lock the door on either side.

1: it's a key that can only be inserted or removed when in the locked position.

2: It can be only be pushed from one side to the other when in the unlocked position

Therefore you can unlock the door on one side to let someone in, lock the door on the same side and remove your key again. Alternatively you can unlock the door then push the key to the other side, lock the door on the other side and remove your key.


This is the original technical document on this key.

That is not correct. This is an essay by sociologist Bruno Latour about the key, not a technical document.

On a side note, what is the rationale behind the fact that there are doors that can be locked without a key? The horror stories of having the door slammed and getting trapped while outside are so common. If a key was necessary no matter what to lock a door, this wouldn't happen and people wouldn't have to spend a kidney calling a locksmith in the middle of the night.

In certain areas, the risk of forgetting to lock the door after returning and having someone unwanted make their way in to the house is higher than the risk of getting locked out after forgetting a key.

There is a larger group of areas where this is perceived to be true, even if it isn't.

I suppose this is now superseded by modern locks, but this is a great example of solving a problem with technology that would otherwise be left up to human behavior. You could ask people to please make sure to lock the door, but there would always be people who would forget, or just not care enough to bother.

"Also, locking an open door is usually not possible."

A good feature to have on otherwise normal doors so that they only ways to lock it is to be inside or outside with the key. I now have a greater appreciation for deadbolts.

The driver's door of most German cars behaves that way too, or used to. For Americans used to opening the door, pressing the lock, then closing the door, this can give the impression the lock is broken.

A lock-only-with-key door would be seriously slow. It couldnt work in high-traffic area, the sorts of places we now use keyless entry.

This is what I did when I moved into my house. Dead bolts only, and dummy handles below.

deadbolts can still have a key on the outside & a paddle-knob on the inside. That's the normal case here in Canada.

Right, but I can't lock myself out with one.

I've actually came across this key in an apartment building in Berlin once, so they really are still in use. The person living there did complain about it though, as (at least in the evening) you had to collect guests from the main gate and escort them back there when they leave, since using the key was the only way to open it. Understandably this is quite annoying when you're living at the fourth floor.

Discovered via tweet: https://twitter.com/historyned/status/1178272006334242819?s=...

Seems like an elegant, physical embodiment of resource acquisition, state management, and release. Albeit uncomfortable in your pocket.

Comparisons to C++ std:: on some of these counts may be valid.

My house in Berlin, the Corbusierhaus[1][2], used to have this type of key for the front (car) gate.

The gate was usually open, and then couldn't be locked with the key. If the gate was closed, it could only be left again in the closed state.

The house is next to the Olympic Stadium, so the gates are closed when there's a football game, concert or other event.

[1] http://www.corbusierhaus-berlin.de

[2] https://en.wikipedia.org/wiki/Unité_d'Habitation_of_Berlin

A bit off topic, but how do you like living in the Corbusierhaus?

I'm reminded of an old Weekly World News article in which a man tiring of losing his keys so often took the drastic step of having a surgeon implant keys at the end of of his fingers, so he could never lose a key again!

The photo they used to accompany the outrageous story was hilarious. Nowadays, that doesn't seem as far-fetched of an idea, with somewhat similar futuristic key implant methods becoming more readily available.

What is the closest crypto analog to this kind of key?

I think it depends how you translate the locking analog. E.g. decrypting your key with {gpg,ssh}-agent keeps the plaintext key in memory in the agent. If the machine reboots or a timeout elapses, the memory is cleared and the key has to be unlocked again.

On-the-fly encryption, Truecrypt as the canonical example, has this property too. The key is always in memory, decrypting text on the fly, but a reboot or period of inactivity will wipe the key.

Probably normal symmetrical key encryption with some kind of companion software.

I think the physical key has the same blade shape on either side.

The companion software would decrypt the ciphertext but prevent exporting the cleartext, forcing the user to first re-encrypt the text first.

Not really crypto but the only thing that comes to mind would be some RAII lock. You have to re-lock the resource as a side effect of leaving the function (dropping the lock). That's a bit far-fetched though.

So Aldi shopping carts and Berlin keys are isomorphic.

You stick your token in, you gain access to a facility, and then to get your token back, you must restore the facility to its proper state. Additionally, in both cases, the facility you're unlocking happens to involve physically moving an object around.

That's all Germany shopping carts, not just Aldi. Though I suppose Aldi has the largest international presence.

It's not just Aldi, the same thing has been common for decades at some Tesco, Morrisons, Lidl etc stores.

This is standard behavior for shopping carts (trolleys) in Australia as well.

The mechanism makes it impossible to forget to lock the door, without also forgetting the key in the lock. Also, locking an open door is usually not possible.

My father lives in Berlin, and before his last move a few years ago he had one of these for his house key. Never knew they were so specific to Berlin.

> The mechanism makes it impossible to forget to lock the door, without also forgetting the key in the lock.

Which I have done, multiple times.

Any sociologists want to summarize the Latour essay?

I'll take a shot.

The subtitle of the essay is "Doing Words with Things", which is a reversal of the famous essay of John L. Austin "Doing Things with Words". Austin pointed out that words have practical effects. Consider the speech act 'I do', when two partners marry: it are the words that have a specific effect in real life.

Now Latour claims that we -- philosophers, sociologists, but others as well -- have to pay attention to the effects material objects have on people interacting with them. He claims that a specific way of acting can be inscribed in an artifact.

So the key is an example of this: you can only take your key out, if you lock the door behind you. Rather than having a message next to the door saying "Please lock the door behind you", this type of behaviour is enforced through the artifact itself.

So social mores or norms can be inscribed in and enacted through material objects (and not just through words).

At least that's an ELI5 version of what the essay intends to convey.

Is there a technical analogue to this?

Why are you posting this? It doesn't appear related to the OP insofar as they are both encountered in Berlin.

Also this clock design seems unnecessarily inefficient. Why divide 24 hours in multiple of 5 hours instead of the much more natural 6? This way it would be a lot easier to decode AM/PM.

I realize that it's about art more than practicality but I don't really understand why that encoding was chosen.

I think it has to do with design. They wanted to make the two top rows have the same amount of lights. Using 6 would mean one row of 6 lights and one of 4. 5^2 is the smallest square that provides enough values to fit 24 hours.

Why not? The post is about weird artifacts in Berlin. This clock may be the key to solving a crypto puzzle.

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