A friend says they are nearby and might drop in. You like them, but you are in the middle of something, the evening was meant to be private or you simply do not want company at that moment. Saying so can feel strangely less friendly than it is.
Make the preference clear outside the immediate situation if possible. “I enjoy seeing you, but please check with me before coming over” separates the relationship from the access arrangement. You are asking for a message and an answer, not withdrawing the friendship.
Be specific about what checking means. Announcing that someone is on the way is different from asking whether a visit works. If you cannot host, say so plainly and suggest another time only if you want to make that plan.
In a shared home, discuss visitor expectations with the people who live there. Guests affect privacy, noise, access and use of common spaces. One person's comfortable spontaneity may create a substantial disruption for somebody else.
You can remain warm at the boundary. “Tonight does not work, but I would like to see you on Sunday” communicates both interest and a limit. You do not need to provide photographs of an untidy room or a full account of your schedule to make the answer credible.
If someone repeatedly ignores the request, address the pattern directly. Do not assume that making increasingly elaborate excuses will teach a rule you have not clearly stated. Where behavior becomes threatening or unsafe, seek appropriate support and prioritize security.
Give visitors a usable alternative: “Please text before setting off, and wait for me to confirm.” A message sent from outside the door does not provide the same choice as a message sent while plans are still flexible. If there are particular days when visits are welcome, you can name them, but you do not need to offer permanent visiting hours to make the boundary legitimate.
Apply the arrangement consistently enough that people can understand it. If someone arrives unexpectedly, you can be polite without turning the interruption into a full visit. In a shared home, agree on the approach with the other residents; your wish for advance notice may intersect with their guests and routines too. The practical goal is that the people who live there have a meaningful say in when their private space becomes social space.
Hospitality is more enjoyable when it is chosen. A home can be a place where friends feel welcome without being a place they can enter whenever they happen to be nearby. Knowing that a visit has been agreed can make you more present and generous once the person arrives, rather than beginning the conversation while privately wishing you had answered the door differently.
A little more room to be yourself.