Most residential doors are pretty "soft" - i.e. easy to get through. There are a number of videos on YouTube where you can see someone almost casually kick in a door - and when you understand the actual support structure around most locks and deadbolts, it's pretty obvious why this is the case. While you might have an awesome deadbolt that resists picking and lock-bumping, the only thing REALLY keeping your door closed is a relatively thin strip of wood (probably pine) and maybe some trim - i.e. the relatively thin door jamb.
This instructable covers one possible technique for making a door frame nearly impervious to being kicked in. I want to admit right off the bat that this design is overkill - lol. I have a tendency to over-engineer things and this project was no exception. If I were to do it again, I'd be looking at using 16GA or thinner metal (1/16") as opposed to the 10GA (1/8") metal I used - it would be easier to work with and still very strong.
I also want to mention that there are commercial products out there that do the same thing - but why BUY what you can MAKE when you can make it better? :) I was also able to make the door reinforcement for about half what a much thinner commercial product would have cost (not including time, of course) - total cost was around $22.
What you'll need:
Metal strip - I used a 2" x 48" strip of 10GA 304 stainless steel. I'd recommend 16 GA (which should be even cheaper)
Heavy-duty screws - 4" long (I used hardened decking screws with Torx heads)
Assorted metal files, hammer, cold-chisel, drill, bits, countersink, sander, sanding belts or sandpaper, measuring tape and/or rule, center punch, scribe, welder, metal saw (reciprocating, abrasive, whatever works) and it would be nice to have Dykem and/or permanent markers.