Close the building door

The door will be by default closed. When you want to enter a building, make sure you close the door again. You do not want to announce to other players if you are in the building, if the open door is clear enough for the enemy. If someone does not know you are inside a building, they may just go in without looking at the situation. Take a look at this bottom gif.

 

It's just to tell you to be careful. (PUBG PC version)

 

How, people in the top gif do not see the situation around and just go into the building, but there is someone there.