Almost everything sold as door security is aimed at the lock, and the lock is almost never what breaks.
A forced hinged door in a British house typically fails in the timber around the strike plate. The plate is fitted with two screws of about 25 mm, which engage the door lining and nothing behind it. A hard shove concentrates on that small area of softwood, it splits along the grain, and the door swings open with the lock still bolted and entirely undamaged, attached to a piece of frame.
That means the highest-value work here costs a few pounds and takes twenty minutes, and no amount of money spent on a cylinder addresses it.
Where doors actually fail
Notice that four of those five are carpentry rather than locksmithing.
The twenty minute fix
This is the single best value job in this whole domain.
- Open the door and look at the strike plate, the metal plate on the frame that the bolt goes into. Take one screw out. It will very likely be about 25 mm long.
- Replace both with 75 mm screws, or longer if the frame allows. These pass through the strike plate, through the door lining, through the packing behind it, and bite into the structural timber of the wall. That is the whole point: you are now fixed to the building rather than to a decorative board.
- Do the same on every hinge. Take out one screw per hinge and replace it with a long one. Three hinges, three screws, five minutes.
- Check for a void behind the lining. There is usually a gap between the lining and the structural stud, packed with offcuts or nothing at all. If it is empty, pack it solid with timber before you screw through, or the long screw simply pulls the lining inwards when loaded.
That is it. No new lock, no drilling out, no specialist. Two screws and some hinge screws, and the door now resists a force that would previously have split it.
Bars and boxes
Once the screws are done, these are the next steps up, in order of value.
A London bar is a length of steel angle that fits over the frame on the lock side, spreading any force along the whole height of the jamb rather than concentrating it at the strike. It is the correct answer to the failure mode described above and it is inexpensive.
A Birmingham bar does the same on the hinge side.
A box strike or security keep replaces the flat strike plate with a deeper box, giving the bolt more metal to bear against and more fixing points.
A hinge bolt is a fixed steel pin in the door edge that engages a hole in the frame when the door is shut. It means that even if the hinges are removed or fail, the door cannot be lifted out on that side. They are cheap and they fit in an afternoon.
On a uPVC or composite door, the equivalent work is different: the multipoint mechanism is usually strong, and the weak points are the cylinder and the fixings of the keeps into the frame. An anti-snap cylinder to a recognised standard, and checking the keeps are screwed into something solid, are the two jobs.
The door itself
Look at the door before you spend anything on the frame.
Tap it. A solid timber or composite door sounds dull. A hollow-core door, which is a cardboard honeycomb between two thin skins, sounds hollow and can be put through with one kick regardless of what is holding the edges.
Hollow-core doors are internal doors. They turn up as external doors surprisingly often, especially on back doors, garage-to-house doors and side entrances, usually because somebody replaced one cheaply.
A door with glazing in or beside it has a different problem: reaching through the broken glass to the handle or the thumbturn on the inside. The two answers are laminated glass, which holds together and takes a long noisy time to get through, and a lock that needs a key on both sides. That second answer conflicts directly with escape, and the next section is about that conflict.
Hinges and the other side
Hinges on the outside are unusual on a front door and common on outbuildings, sheds and old back doors. Exposed hinge pins can be driven out. Hinge bolts, or a set of security hinges with non-removable pins, fix this.
Do not neglect the back. Most households harden the front door and leave a back door, a French door, a utility door, or a door from an integral garage that is markedly weaker and much less overlooked. An attacker picks the quiet side of the building, and so should your attention.
The garage-to-house door deserves specific mention: it is very often a hollow-core internal door with a latch, opening from a space that is itself secured only by an up-and-over garage door. It is frequently the weakest external door in the building while not feeling like an external door at all.
Getting out
Thumbturn cylinders solve the escape problem elegantly and reintroduce the reach-through problem where there is glazing. If there is no glass within arm's reach of the inside handle, a thumbturn is usually the better choice. If there is, either fit laminated glass or accept the key-on-a-hook discipline.
Layers before hardware
Hardware is the last layer and the least important one, which is worth saying on a page entirely about hardware.
- Being seen. Lighting, clear sight lines, a gravel path, no high fence or dense planting screening the door from the street.
- Looking occupied. Lights on timers, no post visible through the letterbox, no obvious pattern of absence.
- Not advertising. Packaging for expensive things broken down inside rather than left by the bin, keys out of sight of the letterbox, ladders and tools locked away rather than left to be borrowed against your own house.
- Neighbours who would notice. Comfortably the most effective measure on this list and the only one that costs nothing.
- Then the door.
The library page this extends, home defence, covers the layered thinking and the legal position. This page is only the carpentry.