11 pm, the guest is at the door
Their train was late. They are outside the building, suitcase in hand, and cannot find the key safe. They message you. You are at the cinema, or asleep, or handling three arrivals at once.
If they scanned the QR code sent with their booking confirmation, they ask "where is the key safe?" and get the answer you wrote: to the right of the main door, behind the meter, four-digit code. In German if they speak German. They get in without waking you up.