The knock at ten past two that was not her
Every daytime booking that goes wrong goes wrong in the same way, and it is never the arrangement: it is somebody who holds a key to your room. They knock at the one moment you had stopped thinking about them.
There is a particular sound that only happens in daylight. Two short knocks, a pause of about a second and a half, and then a key card. Anyone who has stayed in hotels knows it without being able to describe it, and anyone who has had it happen at ten past two on an afternoon they had planned carefully knows exactly how short that second and a half is.
Who it actually is
Usually housekeeping, working through a floor with forty rooms to finish. Sometimes maintenance, sent to look at the thing you reported on Monday and never told when they would come. Sometimes whoever restocks the minibar, which in a good many buildings is a separate round from the cleaning and happens at a different hour. Occasionally a supervisor checking a room that has already been done.
None of them are doing anything unusual. All of them are moving at speed because the round has to be finished by a fixed time, and the pause after the knock is short for the same reason. It is not carelessness. It is arithmetic.
Why the sign fails when it fails
In nine cases out of ten the sign works perfectly and nothing happens all afternoon. The failures cluster into three kinds, and all three are avoidable.
The first is timing. The sign went out at half past one, after the guest had finished arranging the hour, and the round had passed that stretch of corridor at ten to. The trolley was already two doors down. Putting the sign out at nine, before you go anywhere, removes this one entirely.
The second is a sign the guest never found. Newer buildings often use a switch beside the door that lights a small indicator in the corridor, and if you have never stayed in one you will not know to look for it. Step outside once on your first day and check that the indicator is lit. Some rooms only offer the setting inside an app, which works at the system level but is invisible from the corridor.
The third is the thing the sign does not cover. A booked maintenance visit has been assigned to somebody with a slot to fill and they will knock regardless. So will a delivery with a room number on it. If you have reported a fault or ordered anything, the timing can be placed around it, but only if it is mentioned in the thread while the hour is being arranged.
The phone call that solves all of it
Ring the desk in the morning and ask that the room not be serviced today. Fifteen seconds. It is asked for constantly by people who are working in the room, sleeping off a long flight, or unwell, and nobody records it as anything other than a line on a list. Guests hesitate over this call far more than they need to, and the hesitation is the only reason the knock ever happens.
What to do if it does happen
Very little, in practice. Whoever is at the door will apologise and withdraw, because that is the whole of their training for exactly this situation, and they have done it many times this month already. There is no scene, no report and no consequence. The only genuine cost is to the hour, which is interrupted and takes a few minutes to find its footing again.
That is the argument for spending thirty seconds on prevention. Not because anything dramatic follows a knock, but because an hour with a gap punched through the middle of it is not the hour that was arranged, and the whole point of choosing the afternoon was to have the hour be what you intended.
The version of this in an apartment
A flat has no housekeeping and nobody with a master key, which removes the whole problem in one move. What replaces it is smaller and stranger: a parcel courier who buzzes every flat in the building until somebody answers, a neighbour signing for something, or a scheduled meter reading that the owner forgot to mention.
The courier is the common one and the answer is simply to ignore the buzzer, which is what everybody in the building does anyway. The others are worth one message to whoever you rented from, asking whether anything is expected while you are there. A flat with that question answered is the quietest place in this city to spend an afternoon, quieter than any hotel, and the entry sequence written out in the thread is all the preparation it needs.