To install a security door, install hinges at even distances from the edges of the door, measure, and cut the Z bar using a hacksaw. Place the door in the doorway, place a screw inside the upper hole of the top hinge, drill it into the molding, make sure that the door is attached evenly, and secure the door with other screws. Secure the header piece above the door, and attach the expander strip at the bottom of the door.
When cutting the Z bar to the appropriate size, make sure that it is 3/16 shorter than the width of the doorway. Ask somebody to help you put the security door in place, as it might be heavy. Alternatively, one person can hold the door while the other one is making sure that the door fits properly. When drilling screws inside the hinges, make sure that you don't strip the screw. When securing the door in place, make sure that there is a gap about 0.12 inch wide between the door and the floor.
You don't need to drill new holes to install the header piece, as they should have already been put in place by the manufacturer. Use a screwdriver when securing screws in place. Always install the expander piece, as it prevents dirt from collecting at the bottom of the door. Before purchasing a security door, talk to a sales representative to determine your security needs, as security doors come in different levels of protection.