A Klappenschrank was a piece of equipment in the early days of the telephone, that was used to connect two subscribers with each other.
It was operated by a Fräulein vom Amt and was effectively a board made up of holes – one hole per line, covered with a small cap. The caps would flap to show that someone wanted to make a phone call, and often a light bulb would show that a line was still in use. Two holes would be connected by a wire to establish the call between the two parties.
They stopped being used on the telephone network in the western German states in 1966, and in the GDR in 1987.
To hear a simple explanation and a short discussion in German, listen to the podcast:
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