Place a door brace against the door when you are safely inside the room. Door braces are available in many styles, but a common style is a bar that you place at a 45-degree angle from the door to the floor. When in place, the door brace prevents unwanted individuals from opening the door.
Replace the existing door frame with a steel frame. Thieves can gain access to a room, even if the door is locked, by kicking the wooden door frame until it splinters. Purchase and install a steel door frame that thieves will not be able to splinter by kicking. This style of reinforcement also prevents a thief from using a crowbar on the frame.
Replace the door's standard hinges with fortified hinges; standard hinges will not likely provide adequate protection in a situation where the door is being kicked in. Install three large metal hinges that are at least 3 1/2 inches in length and one-tenth of an inch thick. Additionally, secure the hinges to the door frame with long screws that enter the frame by more than an inch. Short screws will not provide enough bracing strength in the event a thief kicks the hinges.
Install a barricade bolt bracket on each side of the door and place a barricade bolt across the door. The bolt's brackets are secured to the door frame with long screws and the bolt itself is a large piece of metal or wood that is wider than the door. When in place, it will prevent someone from opening the door.