Rekeying a lock changes the small pins inside the cylinder so they match a different key. Once those pins are swapped, the old key no longer lines them up and will not turn the lock, while a newly cut key will. The lock body, its finish, the bolt, and the hardware on the door stay where they were. A rekey resets which key the lock accepts, nothing more.
How a key turns a pin tumbler cylinder
The cylinder is the part of the lock your key slides into. Many household door locks use a pin tumbler cylinder, which has a fixed outer housing with a smaller round plug inside it. The plug is the piece that turns when you turn the key.
A row of small holes runs through the plug and housing, and each hole holds a stack of parts. At the bottom sits a key pin, which touches the key. Above it is a driver pin, and above that a spring pressing down. With no key in the lock, the springs push the driver pins partway into the plug, across the thin gap between plug and housing. That gap is called the shear line, and any pin sitting across it keeps the plug from rotating.
The cuts along a key are different depths, and each cut lifts one key pin by a set amount. Because the key pins come in different lengths, only a key whose cuts match those lengths raises every stack until the top of each key pin meets the shear line. Then nothing crosses the gap, the plug turns, and a cam or tailpiece at the back of the plug moves the bolt.
The pattern of cuts on the key is the combination the lock recognizes. The lengths of the key pins are the lock's half of that combination.
What a rekey changes, part by part
Rekeying replaces the key pins with a set whose lengths match a different key. Depending on the lock, some driver pins are changed as well. That is the whole change. The plug, the housing, the springs, the bolt, and the linkage between cylinder and bolt are the same pieces that were there before.
The old key stops working for a plain mechanical reason. Its cuts still lift the pins by the old amounts, but the pins are now different lengths. At least one stack ends up too high or too low, a pin sits across the shear line, and the plug stays put. Nothing has been disabled. The lock simply no longer matches that key.
New keys are cut to the new combination. Spares should be copied from those new keys, since a copy of an old key is just one more key the lock now rejects.
Is rekeying the same as changing the lock?
No. Changing a lock means removing the whole unit and installing a different one, with its own cylinder, bolt, and often new trim on both sides of the door. Rekeying leaves the existing unit in the door and resets only which key it accepts.
A common worry is that rekeying weakens a lock. The design of the lock does not change. The bolt throws the same distance, the cylinder resists turning without the right key the same way it did before, and the knob, lever, or deadbolt looks and fits exactly as it did. A rekeyed lock is the same lock with a different combination.
What stays on your door, and when to ask about a new lock instead
After a rekey, the changes you notice are on your key ring, not on the door:
- The lock, its finish, and its fit in the door are unchanged.
- The bolt, the strike plate it slides into, and other door hardware stay where they were.
- New keys are cut to match the reset pins.
- Every old key is retired, including copies you never got back.
A rekey cannot change what the lock is. New pins do nothing for a cylinder that is worn or damaged, and they add no tamper resistance the lock was not built with. If either of those is the real concern, replacing the lock or moving to a high-security lock is the better conversation.
If you are not sure which side of that line your lock falls on, call Nostrand Locksmith at (516) 644-8976 to talk through whether a rekey or a lock change fits.
Frequently asked questions
Can one key be set up to work several rekeyed locks?
Yes, when the locks share a compatible cylinder and keyway, which is the shape of the slot the key slides into. Each lock is pinned to the same combination, so one key opens all of them. This is called keying alike. Locks with different keyways cannot share a key this way, which is sometimes a reason a lock gets replaced instead of rekeyed.
Does rekeying make a lock more secure, or only change who has a working key?
Rekeying only changes who has a working key. It cuts off old keys, lost copies, and keys held by past occupants, which matters after a move or a staff change. It does not change how well the lock resists tampering, because the lock body and its design stay the same. For more tamper resistance, the lock itself has to be upgraded.
Can a lock that is stiff or damaged still be rekeyed?
A stiff or damaged lock can sometimes be rekeyed, depending on the cause. Rekeying works only on the pins inside the cylinder. Stiffness from a door rubbing or a bolt dragging on the strike is a door hardware question, not a pin question, and needs its own fix. A cylinder that is worn, bent, or broken is usually better replaced, since new pins in a failing lock leave the failure in place.
Do I need to be present at the door when a lock is rekeyed?
Rekeying a lock means working on its cylinder, so whoever does the work needs access to that lock. The person providing access does not have to be you; a property manager or someone you trust can open the door. What matters is that the new keys end up with you, because once the pins are changed, the old keys will not open that door.