Two different problems with two different answers, and people routinely pay for the wrong one.
Rekey when the hardware is fine and the keys are the problem
Rekeying is the answer when the lock is doing its job and the problem is the keys.
A new house, where an unknown number of copies exist. Staff turnover, where somebody left and the key did not come back. A lost key, particularly one lost with something that identifies the address. A relationship ending. A contractor who was given a key for a week in 2019.
In all of these the hardware is fine. It turns smoothly, it is solid, it suits the door. What you want is for the old keys to stop working, and that is precisely and only what rekeying does.
Buying new locks would achieve the same thing at several times the cost, which is why it is worth being clear about which problem you actually have before anyone quotes for anything.
Replace when the hardware itself is the problem
Replacement is the answer when the lock itself is the problem, and no amount of rekeying touches that.
A lock that sticks, drags or needs coaxing. One that has corroded from years of weather until the internals are rough. One that is a light builder-grade unit on an exterior door it was never meant to hold. One that is simply the wrong type - a knob lock where the door needs a deadbolt, or a latch on a door that should never have been fitted with one.
Rekeying any of these produces a lock with exactly the same faults and a different key. The stiffness stays. The corrosion stays. The grade stays.
The useful question is not how old the lock is. It is whether the lock, working perfectly, would be the right lock for that door. If the answer is no, rekeying is money spent on the wrong thing.
How rekeying actually works
The process is worth understanding, because it demystifies why it is quicker and cheaper than replacement.
The cylinder is removed from the lock. Inside it is a stack of small pins of varying heights, and their particular arrangement is what decides which key shape will turn it. Those pins are taken out and replaced with a different combination. A key is cut to match that new combination. The cylinder goes back in.
The door is untouched. The lock body, the handle, the finish, the strike - all stay exactly as they were. Nothing is drilled and nothing is unscrewed from the door itself on most types.
What this means practically is that a house full of doors can be done in a single visit, at the property, without anything being taken away. And when it is finished, every key that used to work is a piece of scrap metal.
How many times can a lock be rekeyed
People ask this expecting a number, and the honest answer is that there is not one.
A sound cylinder can be rekeyed many times over. There is no counter inside it and no point at which the manufacturer declares it finished. What eventually limits it is wear - the plug becoming loose in the housing, the keyway rounding off, the internals no longer holding tolerances well enough for the pins to seat cleanly.
That wear comes from use over years, not from the rekeying itself. Rekeying a lock does not consume it.
In practice, a decent quality lock on a house will accept every rekey it is ever likely to need across its whole life. A poorly made one may already be too worn to rekey reliably the first time you ask, which is not a rekeying limitation so much as the lock telling you what it is.
Getting several locks onto one key
Getting a whole house onto one key is one of the most appreciated things a locksmith does, and it has honest limits.
Where cylinders are compatible - similar type, same keyway, often the same manufacturer - they can be rekeyed to a shared combination so one key opens everything. Where they are not, they cannot, and this is a hardware constraint rather than a matter of effort. A house with a mix of brands accumulated over decades sometimes needs one or two cylinders swapped to bring everything onto one system, which is a small replacement in service of a rekey.
The security trade-off deserves stating plainly rather than being glossed over. One key opening every door means losing that key exposes every door at once.
For most households it is still the right call, because the realistic alternative is not more security. It is a back door that stops being locked because its key lives in a drawer.
Restricted keys, and who can copy your key
Here is the gap that undoes a great deal of otherwise sensible security spending.
An ordinary key can be copied by anybody holding it, at a kiosk or a hardware counter, in the time it takes to buy a coffee. Nobody is asked who they are. No record exists. You will never know it happened.
That means the number of keys to your home is not the number you handed out - it is the number you handed out plus every copy anyone chose to make.
A restricted keyway closes that. The blanks are controlled and not sold openly, and duplication requires authorization from whoever holds the system. You decide who gets a copy, and you know how many exist.
It genuinely costs more, and for many homes standard hardware fitted well is enough. Where it earns its place is anywhere keys have circulated widely: a rental, a business, a house where too many people have had access.
Grades, and what they actually mean for your door
Lock grading gets quoted at people without ever being explained, so here it is in plain terms.
Grading reflects tested durability and resistance - how many cycles the lock survives, how much force it takes, how it holds up to specific attacks. Higher grades are not marketing. They are the results of the lock being put through more than a lower-graded one survived.
What matters is matching the grade to the door. An exterior door on a house takes weather, use and whatever anybody decides to try, and deserves hardware built for it. An interior door on a closet does not, and paying for heavy hardware there buys nothing.
The common mistake in housing across this area is a builder-grade lock on the front door, chosen when the house was finished because it was whatever fitted the hole. It is usually the weakest point on the property.
When it is a business, think in systems not locks
For a business the question is almost never about one lock. Asking it that way is what produces buildings where nobody can say who opens what.
The real questions are: who should open which doors, who should not, and what happens when somebody leaves. A master key system answers all three by design. Each person carries a key that opens only their part of the building, while a master opens everything above it. When somebody leaves, you rekey their level rather than the entire premises.
That structure has to be planned, and planned with room for the business to change - a system built precisely around today's staff list stops fitting within a year or two.
It is worth adding a restricted keyway to it. A carefully designed hierarchy is undone completely the first time an employee copies their key on a lunch break, and on an ordinary keyway nothing prevents that.
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