There has been no lock on the front door of the house for the past few months. I went to Kaiser's for milk and came back to find a new lock on the door. Assumed my old key would not work; buzzed Frau Finke, who let me in and explained that the old key did in fact work. Since I had routed her out anyway this seemed a good time to ask whether I could leave a spare set of keys with her, in case I got locked out. Frau Finke (goodhumouredly): Ja, das ist Ihre Spezialität. This seemed a bit hard - I haven't been back to the Schlüßeldienst in years, seems like - but the main thing is, a spare set is now safely with the concierge.
This may be a useful precaution. Now that I am immersing myself in Python, Unix and R I find myself losing track of practical details; I forget that there is something on the stove and come to only to find caramelised broccoli in a charred pan, this sort of thing.