Please knock at the door.

Kindly remind others to knock at the door.

1. If you have a secretary, ask him to make an appointment with the secretary next time and ask him to remind him.

2. Take the backward as the forward: If you come in without knocking at the door, just say "I'm sorry, I didn't hear your knock at the door and kept you waiting".

Remind me in a humorous way that my door has recently gone on strike, which often makes me unable to hear the knock at the door. Looks like I have to talk to the door.