Your frame is weaker than your lock.

A locked door is a system with four parts: the lock, the bolt, the strike, and the frame. Force applied to that door has to defeat whichever of the four is weakest. It does not politely attack the part you spent money on.

The market is built around the first two. Locks are a product with a brand, a grade, a box and a price, and they can be marketed. Grade 1, Grade 2, hardened inserts, anti-drill pins, anti-pick pins, all of it real engineering, all of it addressing attacks on the cylinder. Frames are not a product. Nobody sells a frame upgrade. There is no box for it.

The result is a market where the strongest link gets all the attention and the weakest gets none. Almost nobody picks a residential lock in the real world; picking is slow and takes practice. What happens instead is force, and force finds the trim.

Consider what the two sides of the door are actually made of. The bolt is hardened steel and the cylinder is brass and steel. The trim is a softwood board perhaps three-quarters of an inch thick, nailed in place, holding two short screws in end grain. There is no contest, and this is why the aftermath so often shows an undamaged lock, an undamaged bolt, and a splintered strip of wood on the floor.

A three-inch screw changes the geometry entirely. It passes through the trim and lands in the stud, framing lumber, part of the house's structure. Now force has to break the actual building rather than a decorative board. The lock has not changed. What has changed is that the lock is finally attached to something.

The same reasoning applies to the hinge side, and that side is forgotten even more consistently. Hinges are fitted with the same short screws into the same trim. A door forced at the hinges fails identically, and hinges are almost never mentioned in a security conversation.

There is a second reason this stays invisible, and it is worth naming. Nobody inspects it. A home inspector checks that the lock operates. An insurer asks whether the door has a deadbolt, not what the deadbolt is screwed into. A locksmith called for a rekey has no reason to raise it unless they choose to. So a weakness that takes four minutes and a few dollars to eliminate survives decades of ownership, surveys, sales and renovations, because at no point does anyone whose job it is to look actually look.

The practical test is the one at the top of this page, and it takes one screwdriver. You do not need to trust anybody's assessment, including ours. Back a screw out and measure it. Everything in this guide follows from what you find.

• Three-inch screws in every exterior strike plate. A few dollars, minutes a door, and it converts the most common failure mode into a non-event. Nothing else on this list comes close on value.
• One three-inch screw per hinge leaf. The centre hole. Three hinges per door. Now both edges of the door are anchored to structure rather than trim.
• A reinforced box strike. A heavier plate that spreads load across more of the jamb, often with a cup that captures the bolt. The proper version of step one.
• A real deadbolt where there is only a knob lock. A knob lock is a spring latch with a keyway in it, defeated with a card by somebody with no skill. Common on post-war Delaware housing as the only lock on the door.
• Deal with the garage entry. Unheated, unweatherproofed, cheapest lock on the property, behind a garage door that is often the easiest way in. Consistently the biggest gap in an otherwise sensible house.
• Patio and slider hardware. The factory latch on an older aluminum slider is pressed metal that gives up under a shoulder. An auxiliary foot lock or keyed slider lock is inexpensive.
• Only then, better cylinders. High-security cylinders solve picking and drilling, which are real but rare. They do nothing at all about a splitting jamb. Spend here last, not first.

The age of the framing. Wilmington Manor, Brookside, Collins Park, Penn Acres and the rest of the post-war build went up in the 1940s and 1950s. That framing is old softwood that has been drying for seventy or eighty years, and dry old softwood splits more readily than fresh lumber. It is also the era in which short strike screws were simply the standard, nobody was cutting corners, that was how doors were hung. Which means an entire generation of Delaware housing has the same weakness, installed correctly to the practice of its day.

The moisture. Delaware is a coastal plain state and the humidity is relentless. Jambs near the river and the marsh, Newport, Edgemoor, Delaware City, Leipsic, Little Creek, take on and shed moisture year after year, and repeated wetting and drying degrades timber's ability to hold a fastener. A short screw in a jamb that has cycled through sixty Delaware summers is holding considerably less than it was when it went in.

The row homes. Wilmington and Elsmere front doors open directly onto the pavement with no porch, no storm door and nothing between the frame and the weather. Those jambs get rain, road salt spray and freeze-thaw directly, every winter, for a century.

The new builds. Middletown, Townsend and Cheswold subdivisions are the opposite case and the same outcome. The framing is sound and modern, and the strike screws are still three-quarters of an inch, because that is what comes in the box with a builder-grade lock set. New house, same gap, and it is fixed in four minutes.