Why did the male prisoner call the police before entering the detention center police office?

First, you should knock on the office door. The door is closed. The forefinger bent and knocked on the door three times. Its special department is better than the school team. In addition to knocking at the door, you must also call to report. Pay attention to knocking at the door. Knock on the door three times and find that it is forbidden to enter the door. Wait or choose another room.