Everything You Never Knew You Wanted to Know About Berlin


According to the records of the Berlin Statistical Office in December 1900 the population of the city reached 1,888,848 inhabitants. Considering that in 1845 Berlin registered only 442,500 residents, the number of people living in Prussia’s capital grew in less than five decades  by the staggering 1,446,848! .

Such rapid growth of population, although a welcome development from the point of view of employers, the services and property owners, brought with it some quite serious issues. Lack of payable accommodation which eventually led to property speculation and riots (such as those in Moritzplatz in 1863, described in the following post), lack of proper sanitation that caused diseases to spread through densely populated poor areas of Berlin like forest fire in rain-free July, and crime levels sky-rocketing all over the place. Safety was becoming more and more of scarce goods.

One of the commoner problems those days were break-ins: burglars had it much easier now that the tenants changed so quickly that one hardly had time to get to know the neighbours. Houses were full of strangers, which made it very easy for thieves to enter unnoticed. One way of keeping them at bay was simply locking the main entrance door. Sounds uncomplicated but it wasn’t.

Even though each house was traditionally locked up by the Hausmeister (concierge) in the evening and sometimes even remained locked during the day, many tenants who also had the main key “forgot” to turn it in the lock again after entering the building. Burglars rarely refused such a kind invitation.

In order to force people to lock the doors behind them a 24-year-old Berlin locksmith Johann Schweiger came up with a brilliant idea: a key that had to be turned again on the other side of the door in order to be able to pull it out of the lock at all.

berliner schlüßel with a key-ring

Berliner Schlüßel with a special key ring to attach it to a bunch of other keys

The unusual looking key had no bow – the thing you would normally hold with your fingers when using it – but it had two so called “bits” (Bärte) instead. After putting the key in the lock, you had to turn it, walk in, close the door, turn the key and only then were you able to take it out of the lock again. It solved the problem splendidly but coming back home from the local pub at night became a bit of a challenge.

Schweiger’s invention was christened Schweiger-System and the key became famous as Berliner Schlüßel or Doppelsteckschlüßel. For years afterwards it was blessed and cursed by generations of Berlin tenants. It became the most popular locking system in town but failed to convince the house-owners in other German cities.

Berliner Schlüßel invented by Schweiger in 1912 was granted a patent only 13 years later, on February 15th, 1925. And now in order to do away with an old misunderstanding repeated by numerous newspapers and published on many a web-page, the following needs to be said: Berliner Schlüßel does not come from Wedding (with all due respect to the fellow borough in the North). And neither did the company that made it.

Johann Schweiger

Johann Schweiger as the head of Alfred Kerfin & Co. (photo:

It is quite likely that Johann Schweiger himself came from Wedding: Berlin Directory for 1913 names one Schweiger, Johann, Schlosser as a resident of the house in Stettiner Strasse 5. If it’s the same Johann Schweiger is hard to judge – there doesn’t seem to be another locksmith of that name in the book, though. What’s certain, however, is the fact that the company he sold the idea to and which he took over in the same year as Schweiger-System was registered at the Kaiserlicher Patentamt in Gitschiner Strasse was very much not from Wedding.

Berliner Schlüßel was first produced by Türschließerfabrik Alfred Kerfin & Co from Kreuzberg. The company, established by (this might come as a surprise) Alfred Kerfin, the man whose name it is still bearing today, had its original seat not far from the patent office: in Gitschiner Strasse 63 (the second floor in the second Hof or “courtyard”, telephone available).

Alfred Kerfin & Co. in Gitschiner Strasse 63 (Berliner Adress Buch 1894)

Alfred Kerfin & Co. in Gitschiner Strasse 63 (Berliner Adress Buch 1894)

The location of the first company seat in Gitschiner Strasse 63 (gone today)

The location of the first company seat in Gitschiner Strasse 63 (gone today)

In 1912, the year of Schweiger’s invention and the same year he took over the running of the company, Kerfin & Co were already occupying bigger rooms in Adalbertstrasse 7, also in Kreuzberg. According to the company chronic, they stayed there until 1940 when their workshops burnt down and Johann’s brothers Friedrich and Joseph (Johann’s son chose to relinquish his right to the running of the successful family business) decided to move the company to Liebenwalder Strasse 39. In Wedding.

Berlin Registry entry from the year 1915

Berlin Registry entry from the year 1915

Today Kerfin has its seat in Sophienstrasse in Berlin-Mitte. The Schweiger family sold it in 2011 after almost exactly 100 years of passing it over to their own.

As for the key itself, it lost its popularity with the division of the city in 1961 (the company could not deliver or maintain the Schweiger-System in East Berlin) and then again when intercoms or doorphones became a regular feature.

Despite this, those who moved to Berlin in the 1970s or 80s were still quite often confronted with the object handed to them by the landlord and whose purpose often seemed to escape them. You can read an amusing account of such an encounter in Der Wedding, The Magazine for Daily Culture but be warned: it’s in German AND it ain’t gentle in the vocabulary department. Still it is one of the funniest man-against-the-berlin-key tales available online.

Surprisingly enough, despite it inconvenient size and being a clear offence to one’s personal freedom (in the I-World we all live in a key that forces you to lock the door behind you must be a pain in the wrist for many), there are still around 7,000 such keys in use in the city. Although some of them found a second life as well.

 For example as the so called “trackable item” for the game know as “geocaching” (all terms explained here): one lucky Berliner Schlüßel was sent on a long trip around Europe, starting at the former Tempelhof Airport in Berlin and making stop-overs in Spain, Denmark and Austria. During its 3,546.4-mile long journey it returned to Germany and left it again, only to vanish without a trace in Switzerland. Considering how very focused on keys, locks and safety the Swiss traditionally are, you could  say with a sigh: “Out of all places…”

And here is a little film made by ARTE as part of the Karambolage series and devoted to the curious Berlin invention. Even though it is in German also the non-speakers will get the gist of it.



  1. lostfunzone
    Mar 6, 2013

    very interesting read. a friend of mine (in wedding) still has to use a berliner schluessel today.

  2. berlioz1935
    Mar 6, 2013

    Finally something about Kreuzberg again. 🙂

    • notmsparker
      Mar 7, 2013

      I couldn´t agree more::) On the other hand, isn´t everything about Kreuzberg anyway?;-)


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