If you are interested in protecting the room while you are inside (thus protecting you and your possessions), then you might try a small wood wedge placed between the door and door frame on the floor. This will keep the door from opening inward against repeated attack. Obviously, it can also be used to prop a door open, should the need arise. Also, ground floor rooms are more vulnerable because of the windows and also ease of escape. If the robber has to go up and down an elevator or stairwell, there is more chance that he could be cornered or caught. Of course, you are also further away from your escape route if there should be a fire or other emergency.