Time to break for lunch, he thought, when a guard knocked at his door.

The guard took them through that door to another, stopped and knocked.

Here was about the only place in this apartment where the guards wouldn't just knock and walk in.

On the second floor, we stopped before a heavy wooden door and the guard knocked upon it.

A guard knocked and opened the door, urging him to hurry as the meeting was about to begin.

Julius was deep in work when the guard knocked on the door to his rooms.

Some distance down the corridor, the guard stopped at a door and knocked.

The guard stopped in front of Valenti's office and knocked once.

The surprised guard again knocks him to the floor.

The guards now knock on his door from time to time to ask whether he needs help with anything.