What a new key changes, and what it leaves alone

A lock has no idea who is standing at the door. It reads depths cut along a blade, and it turns when those depths lift a stack of pins to one shared line. Rekeying swaps that stack for a different set, so a new pattern reaches the line and the old pattern stops short. The door keeps its hardware. Finish, fit, the throw of the bolt, the way the latch meets the strike — all of it sits where it sat before the plug came out.

Some residential cylinders skip the disassembly entirely. Kwikset SmartKey and similar designs are built to be rekeyed with a tool and an existing working key, which is a different procedure with the same outcome. Either way, what you are buying is a revocation. Every key cut to the old pattern becomes a piece of metal that fits the keyway and stops there.

Worth naming the flip side plainly: nothing about the door got stronger. The frame, the strike screws, the length of the bolt and the glass beside it are all as resistant as they were this morning, because a pin stack has nothing to do with force.

Ask how many keys exist for a door and you get a number pulled from memory: two at closing, one to the sitter, one on the hook by the fridge. That number counts keys that were issued. It does not count keys that exist, and the gap between the two is not knowable, because an ordinary key can be copied at a hardware counter with no record of who copied it. A copy leaves no mark on the original. Nobody has to mention it afterward.

So "I got the keys at closing" answers a question that was never the right one. Keys handed over are keys somebody chose to hand over. A prior tenant, a contractor who needed access for a week, an ex with a spare in a glove box — none of them appear on that list, and none of them are obliged to. Turnover, not suspicion, is the sane trigger for a rekey, which is why rental turnover rekeys in Dartmouth belong on the move-out checklist beside the paint touch-ups rather than waiting on a reason.

If uncontrolled copying is the real problem — and for a rented unit or an office it often is — rekeying alone resets the count without stopping it from climbing again. A restricted keyway raises the bar. Its blanks are distributed only to authorized dealers, so a routine copy at a hardware counter is off the table, and what copying remains is traceable and impractical rather than impossible — the control is strongest on a patented keyway still under protection. That is a hardware decision rather than a service visit, and it is the closest honest answer to the question of who can make another key tomorrow.

Rekeying changes who can open a door. It does not change how much force that door will withstand, and it has no opinion whatsoever about a window, a garage remote, or a slider with a panel that lifts out of its track. If someone came in through a ground-floor window, a new key list closes nothing.

Push on this before booking, because the two problems feel identical from the inside and are not. One is access control: keys are out there, and you want them dead. The other is resistance: the door came open under force, or would, and the key list is beside the point. Rekeying answers the first cleanly and does nothing at all for the second.

When the honest read is resistance, the work moves to the hardware itself — a better cylinder, a strike screw long enough to reach framing instead of jamb trim, a deadbolt with real throw behind it. That is lock and deadbolt installation, a different job with a different result. We would rather say so at the door than pin a cylinder that was never the weak point.

Rekeying assumes a mechanically sound cylinder. Pin a worn or corroded plug and the new key binds exactly the way the old one did, which reads to anyone holding it as botched work. What actually happened is a good key cut for a bad lock.

Salt air keeps this question live here. Exterior doors along the South Coast take coastal exposure, and the internals matter: parts specified for coastal or marine exposure outlast standard zinc-alloy internals in that air, and thin plated finishes on an exposed door corrode visibly long before ones rated for coastal service do. A cylinder that has been breathing salt spray for years can already turn stiff with the correct key in it.

We check the plug before quoting the change, not after. The signs that push a door toward replacement instead: a key that needs jiggling to find its position, a plug that grinds through part of its arc, green bloom on the cylinder face, springs that no longer return the pins cleanly. Rekeying a lock in that state buys a faithful reproduction of the complaint you started with.

Cylinders sharing a compatible keyway can be keyed alike, so one key runs the front door, the back door and the basement. Doing them in a single visit adds little labor, because every cylinder is already open on the bench — the rest is reading the bitting and setting pins to match it.

Triple-deckers make the idea concrete. The characteristic multi-family house of southern New England mill cities stacks three units over one common entry, each unit behind its own door, so a single building carries several cylinders that may or may not share a key. What an owner usually wants there is a split: one key for the common entry, a separate key per unit, and no unit key that opens anything but its own door.

Past a certain number of doors that stops being a key and becomes a schedule — which cylinder answers to which key, who holds what, and what happens the day a holder leaves. That design work sits behind commercial master key systems, and it pairs naturally with a restricted keyway, since a keying chart is only as good as the control on the blanks. Ask for the layout first. Pinning is the easy part once the chart is right.