I sold commercial doors, and security hardware to go with them.
The primary goal is to keep the door jamb from being spread far enough apart to defeat the locking mechanism - which includes the hinges. Long screws aren't enough, and residential grade is basically useless. In security applications, the walls on both sides of the openings need reinforcement back to the next two - 2 - studs, at least 32 inches. Which means NO sidelights or windows. A window next to the door defeats everything you do.
Tying the jambs horizontally to the studs imposed enough resistance to prevent spreading them. Second, the hinges need to be interlocked to the jamb - use studded screws that project a pin into the opposite hole, or hinges with tabs/pins that do so. Metal jambs aren't necessarily stronger, especially if they are hollow - ensure they are correctly anchored, and have them filled to prevent moving them apart their combined depth, which is enough to pry the bolts out of their recesses. If an outward swinging door, the hinge pins also need to be secured.
On the lock side, double dead bolts at top and bottom are needed, the latching mechanism should be a mortise lock - they project solid bolts, not pressed steel composites that are easy to bend. The lock recesses should be armored to prevent simply cutting it them out and allowing the door to swing open. The door itself needs to be welded seam construction - if the outer skin can be pried up and away, so can the inner skin. Gauge is also important, a 22 ga lightweight residential door has no security rating. It starts at 14 ga, and 12 gauge doors have actually been defeated by determined 14 year olds in counseling centers.
As for keying, any commonly available key sold for residential use is a joke, every BigBox and hardware store will duplicate them without question. Get a security keying from a commercial locksmith that cannot be purchased except thru authorized outlets. Mark the keys so you know who lost theirs, and if lost, rekey. Let them pay the bill, they will learn on the spot. If they can't be trusted with the key, they shouldn't be home alone with it, either.
All this can be defeated by simply finding a more obscure entry point - the existence of cordless tools means a determined attacker will simply cut a hole thru the outer wall, which frankly, is easier. They just aren't that smart, usually. And that includes the roof.
As an example, one perpetrator beat in the back door on a business, stealing items inside. The door was located across an alley in a residential neighborhood, no one called the cops, although the sound of them striking the door and jamb with a sledge hammer and prying it open with a crowbar should have been. The ironic point is that the building was sheet metal, five minutes with a drill driver and some bending, they could have gotten in without the noise and a whole lot more time. Ya can't fix stupid.
A desire for security is a red flag in many situations - there are good reasons to do it, but you have to ask, what suddenly became so much more attractive to want to break in? Someone is showing off too much personal wealth to the wrong people, and were clueless about the deterioration of the neighborhood or unwilling to take a small loss early and just move out. Sometimes personal circumstances change, too - at which point it's not going to be just a door that needs changing. Cut back the shrubbery, add lights, and being proactive about the neighborhood security is better than living with drug dealers and prostitutes literally on your steps.
One thing is guaranteed - neighborhoods change. Nothing stays the same, be aware of what is going on, is it maturing with years left to grow, or deteriorating? One of the first clues is watching an older couple pass away and seeing the children put it up for rent. Sorry - flame on - it's the worst thing that can happen. You now have absentee landlords and residents with no care to see the property maintained. It's the end of a peaceful neighborhood, and within 20 years, it's too late to lament.
We saw our property values stall in those circumstances, and were lucky to get out - the next owner remodeled the kitchen and broke even, the one after that can do nothing but watch others drag down the values.
If you are thinking security doors and needing to keep out certain people, then you are already behind on a successful defense, which is to live somewhere it simply never happens.
