I have used the Armor Concepts door hardening kits - easy to install and seemed like they will perform as advertised - no one has tried to break in so far thank goodness. FYI - you can look around the Amor Concepts site and they often have blems, closeouts, etc. at great pricing. I have the kits on my basement entry door and two other exterior doors. In the basement, I have a "double personnl door" that is difficult to "harden" with these type kits so I bought two sets of metal brackets such that I can install two 2x4 boards across the door for extra security. I added two sets of brackets to the basement entry door to hold 2x4s also along with the Armor Concepts kit.

However, our primary deterrent is two "attitudinal" Daschunds who hear everything and bark at everything!