The lock you are actually rekeying
Most house keys work with a design called the pin tumbler. It has been the standard for residential locks for a long time because it is compact, reliable and simple to produce. When you look at a keyway from the outside, you are looking at the front of a small cylinder made of two main parts: a fixed outer housing and a rotating inner core called the plug.
The plug is the part your key slides into, and it is the part that turns when you turn the key. It is held in place by the housing, and it is prevented from turning by a set of small pins that cross the line between the plug and the housing. Those pins sit in drilled channels, usually five or six of them in a row, and each channel holds a stack of pins pressed down by a tiny spring.
When the lock is locked, the pin stacks bridge the gap between the plug and the housing, so the plug cannot rotate. When the right key goes in, the cuts on the blade lift each pin stack to exactly the right height, so the gap between the pins lines up with the gap between the plug and the housing. This line is called the shear line. When every stack is aligned at the shear line, the plug is able to turn, and the lock opens.
Rekeying is simply changing the pins so that a different key, with different cut depths, aligns them at the shear line. The plug, the housing, the bolt, the handle and the finish are all the same. What changes is the arrangement of the small parts inside the plug.
What the pins and springs do
In each channel there are generally two pieces of metal. The lower piece is called the key pin, and it touches the key. The upper piece is the driver pin, and it sits above the key pin in the housing and is pushed down by a spring. Together, the two pins make a stack, and their combined height is fixed by what is inside that channel.
Key pins come in a range of lengths. A longer key pin is lifted less by a given cut, while a shorter key pin is lifted more. When the cuts on a key match the key pin lengths in the lock, each stack is raised until the break between the key pin and the driver pin sits exactly at the shear line. That is the moment the plug can turn.
The springs give the system its action. They press the pin stacks down toward the key, which is why you can feel the key push slightly against resistance, and why the pins settle back when the key is withdrawn. Without them, the pins would not return to their locked position.
This is the reason a copied key that is slightly off can feel gritty or may not turn at all. If one cut is a fraction too deep or too shallow, one pin stack does not land at the shear line, and the plug stays locked. It also explains why worn keys can eventually fail: the cuts erode, and the heights drift away from the pin lengths in the lock. Our guide on how key cutting works goes deeper.
Step one: getting access to the plug
A rekey begins with removing the lock cylinder from its hardware, or, in some cases, working on it while it is still mounted. For a deadbolt, the technician usually takes the lock off the door so that it can be worked on at a clean surface, though experienced technicians can do certain locks while mounted. For a knob or lever, the cylinder is removed from the handle, often by releasing a small retaining clip or tab.
Once the lock is open, the technician needs to take the plug out of the housing without letting the pins and springs fly out. This is the delicate moment. The plug is pushed out with a dedicated tool called a plug follower, a short rod the same diameter as the plug. The follower pushes the plug out of the front of the housing while taking its place, so that the pins in the housing stay in their channels and are not scattered.
Without a follower, the pins and springs can spill, and some may be lost or put back in the wrong order. A technician working with the right tools avoids this. It is one of the reasons rekeying is quick for a trained person and frustrating for someone doing it for the first time with a kit.
Many locks also use a small retaining ring or clip at the back of the plug that has to be removed first. Specific designs vary by brand, and a technician who sees many brands knows where to look. If you rekey many locks, you get familiar with the quirks of each one.
Step two: swapping the pins to a new arrangement
With the plug out, the key pins can be removed from their channels in the plug. The old key pins are matched to the old key. The technician replaces them with new key pins of lengths chosen to fit a different key. The driver pins and springs, which sit in the housing, usually stay put, although some work includes checking them.
The new arrangement is chosen for the new key. A rekey kit includes a range of key pin sizes, and the technician selects a combination that corresponds to a key that can be cut on a standard machine. There are many possible combinations, though the lock manufacturer sets the limits on what combinations are allowed for a given keyway.
Each new pin is seated in its channel and checked. The technician makes sure it moves smoothly and does not bind. Springs are checked for tension and condition. If a spring is weak or a pin is worn or bent, it is replaced at this stage, because a lock with a faulty spring can give trouble later.
Then the plug is reinserted into the housing, using the follower again in reverse, so the housing pins stay in place as the plug goes back. The retaining ring or clip is replaced. At this point, the lock has a new internal arrangement, and the old key no longer lines up the pins at the shear line.
- Plug follower used to keep pins and springs from spilling.
- Old key pins removed and replaced with new lengths.
- Driver pins and springs inspected and kept or replaced.
- Plug returned to the housing and retaining clip refitted.
- Old key tested to confirm it no longer turns.
Step three: cutting and fitting the new key
A new key is cut to match the new pin lengths. Each cut on the key blade has a depth, and the depth at each position corresponds to a key pin length in the plug. A technician uses a key cutting machine, which can set depths precisely, to produce a key that lifts each pin to the shear line.
The new key is tested in the rekeyed lock. It should slide in smoothly, turn without catching, and return without drag. The technician also tests the old key to confirm that it does not turn. This is the proof that the rekey worked. If the old key still operates the lock, even partially, something is off, and the work is checked again.
If several locks are being rekeyed to the same key, the technician uses the same pin arrangement in each cylinder, so one key operates them all. This is called keying alike. It works within the limits of the brands and keyways: locks of the same brand and keyway are generally easy to match, while locks from different makers may not be compatible. Our guide to keyed alike locks covers the details.
Finally, the new key is tested in the lock after it is back on the door, because alignment on the door matters as much as the key. A bolt that binds on the strike plate can feel like a bad key even when the key is perfect. The technician checks the whole action: key, plug, bolt, and latch.
What changes and what stays the same
The things that change are small. The key pins inside the plug are different. The key that opens the lock is new, with new cut depths. Old keys no longer work. In some cases, the springs or some parts of the pin stack are refreshed.
The things that stay the same are most of what you see and use. The lock body, the handle, the deadbolt, the faceplate, the finish, the bolt and the strike plate all remain. The strength of the lock is not changed. The brand and the keyway remain the same, which means that anyone with a blank for that keyway and the correct cut information could produce a copy of your new key, so key control still matters.
Another important point is that rekeying does not repair other problems. If the lock was sticky because of worn parts or corrosion, rekeying will not cure that. If the bolt was short or the strike plate weak, they stay that way. This is why a technician checks the overall condition before proceeding, and tells you if replacement would be better. Our rekey or replace guide helps with that decision.
One more thing that stays the same: the number of keys the lock can accept is not unlimited, but a rekeyed lock can be cut for as many copies of the new key as you need. Plan to have spares made from the new key right away, and keep track of who receives them.
Locks that are harder or impossible to rekey in the usual way
Not every lock follows the simple pin tumbler pattern. Some cylinders are sealed or designed so that the user cannot access the plug, and some require factory service. Some budget locks use designs that are not meant to be rekeyed, and replacing them is simpler. A few brands have unique systems with their own tools, and in those cases a technician may use the manufacturer's method or recommend replacement.
Mortise locks use a separate cylinder that screws into the lock case. The cylinder can usually be rekeyed in the way described above, or swapped for another cylinder, and the lock case itself stays in the door. See mortise lock service for more on that.
Smart and electronic locks often include a keyed backup cylinder, and that cylinder can be rekeyed. The electronic side is changed separately, by updating user access, which is not a mechanical process. High-security cylinders, with restricted keyways and added security pins, can be rekeyed by someone with the right parts and authorization. Our high-security cylinders page explains the limits.
Master key systems add another layer, with extra pins that let two different keys open the same lock. Rekeying within such a system takes planning and good records, because changing one cylinder can affect the hierarchy. If your building uses a master system, say so when you call.
Why a trained technician makes a difference
Rekey kits are sold for do-it-yourself use, and some people do manage them. The task is within reach of a patient person, but there are many places to go wrong. Pins can be mixed up, springs can be lost, and a plug that is reinserted without a follower can scatter parts. A lock that is reassembled with a bent spring or a misplaced pin may feel fine at first and fail at a bad moment.
A technician brings experience with many brands, tools that are designed for the job, and a stock of parts. They also check things that a kit does not tell you to check, like bolt alignment, strike plate condition, and the wear on your existing key. They can spot a lock that should be replaced instead.
There is also the matter of key making. A new key needs to be cut accurately. A key that is a hair off may work in the lock for a while and then bind or wear the pins. A mobile technician carries cutting equipment and can produce a precise key at your door, and make copies from the new key on the spot.
None of this means a careful homeowner cannot rekey a simple lock. It means that the risk of a misstep is real, and the cost of a misstep is usually a lock that has to be replaced anyway. If you want the work done right the first time, it is worth having a professional do it.
What to expect at your door and how to prepare
When the technician arrives, they will confirm who you are and that you have authority over the locks. They will look at each lock, check the brand and condition, and explain what they will do. They will work on one lock at a time, testing as they go, so that you are never left with an unlocked door.
You will be asked about how many keys you want, and whether you want some doors keyed alike. It helps to decide ahead. If you have a preference for keeping separate keys for separate doors, say so. For rental properties, think about whether a key system makes sense.
Before you call, gather the facts: how many locks, which doors, what types, and whether any are stiff or damaged. Have the existing keys handy, because they help the technician test the old arrangement and confirm it is fully changed. If you have lost keys, that is fine, and rekeying does not require the old key.
Quotes are given by phone. Complicated jobs, such as unusual hardware, large sets of locks or master key systems, may need an on-site visit before a final quote, and there is a service call charge that is explained on the phone before dispatch. When you are ready, call and we will talk through what you have and what you want, and answer questions about how the process would work at your property.
Questions people ask
Do I need the old key to have a lock rekeyed?
No. A technician can rekey a lock without the old key, because the work involves opening the cylinder and changing the pins. Having the old key can make testing easier, but it is not required. If you have lost every key, say so when you call and we will explain how the job will be handled.
Will the new key look different from the old one?
The new key will have different cut depths, so the pattern of ups and downs on the blade will be different. If the lock keeps the same brand and keyway, the blade shape will match. You may notice that the key looks similar in shape but is not interchangeable with the old one. That is how it should be.
Can all my locks be made to use the same key?
Often yes, if the locks are the same brand and keyway, or if they can be set up to match. Some mixed brands are not compatible and may need replacement for one or two doors. A technician can tell you what is possible after looking at the locks, and can suggest the simplest way to reach one key.
Is a rekeyed lock as secure as a new one?
A rekeyed lock is as secure as it was before, in terms of strength, and it stops old keys from working. It does not become stronger. If the lock was a good one in sound condition, that is fine. If it was basic or worn, replacement may give you better protection. We can explain the difference when you call.
Can someone copy my new key easily?
If your keyway is a common one, a key shop can cut copies from your key, so key control still matters. Restricted keyway systems limit who can make copies. If controlling duplication is important, such as for a rental or office, ask about restricted systems. For a typical home, a careful approach to who holds keys is usually enough.
How much does rekeying cost?
Quotes are given by phone, because the cost depends on the number of locks, the brands and the condition of the hardware. Simple jobs can often be quoted fully on the call. Complicated jobs may need an on-site visit, and there is a service call charge that we explain before anyone is dispatched. Call and we will walk through it.
Describe the situation by phone and we will tell you what the job involves. Quotes are given by phone. Jobs that cannot be quoted without seeing them need a technician on site, and the service call charge is explained on the phone before anyone is dispatched.
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