All outside doors should be metal or solid wood. If your doors don't fit tightly in their frames, install weather stripping around them. Install a peephole or wide-angle viewer in all entry doors so you can see who is outside without opening the door. Door chains break easily and don't keep intruders out. Check the outside Look at your house from the outside.
Thieves hate bright lights.
Install outside lights and keep them on at night. Keep your yard clean. Cut back tree limbs that a thief could use to climb to an upper-level window. If you travel, create the illusion that you're home by getting some timers that will turn lights on and off in different areas of your house throughout the evening. Lights burning 24 hours a day signals an empty house.