When you move into a newly built home, you're usually given a set of keys at handover. You might also be told that once you use your new key, the builder's key will no longer work.
That's called construction keying, and it's actually a clever system.
It allows builders and tradespeople to access properties during construction without needing a separate key for every house. Once the homeowner takes possession, their key activates a mechanism inside the lock that permanently disables the construction key.
It's convenient for everyone, and it generally works exactly as intended.
But there's something I've noticed when rekeying these locks over the years. Even after the builder's key has been disabled, there can still be unnecessary master pins left inside the cylinder.
Those pins no longer serve their original purpose, yet they can leave additional possible key combinations that operate the lock.
And personally, I don't see a good reason to leave them there.
How Does Construction Keying Work?
During construction, a builder may have multiple homes underway at the same time. Electricians, plumbers, painters and other tradespeople all need access.
Rather than carrying a different key for every property, a construction keying system allows a designated builder's key to operate compatible locks throughout the building stage.
In certain residential systems, the lock contains a small ball bearing, sometimes called a construction ball or project ball.
When the homeowner turns their permanent key for the first time, this ball drops into a separate cavity inside the cylinder.
That changes the internal keying arrangement, preventing the builder's key from operating the lock again.
The homeowner can now use their own key without replacing the entire lock.
It's a practical solution, and I'm not suggesting that the system itself is defective.
What Happens to the Other Master Pins?
This is where things become interesting.
Inside a conventional pin-tumbler lock, the key lifts a series of pins to the correct heights. When everything lines up at what's called the shear line, the cylinder turns.
In a master-keyed arrangement, additional small pins, known as master pins, can create more than one shear line within a pin chamber. This allows different key combinations to operate the same cylinder.
In some construction-keyed locks I've worked on, the project ball drops out of one chamber when the homeowner activates their key. However, master pins can remain in several of the other chambers.
The construction key no longer works because one chamber can no longer line up for that particular key.
But the remaining master pins still create additional shear lines in the other chambers.
When several chambers contain master pins, the different shear lines can create multiple possible operating key combinations.
In other words, the builder's key may be permanently disabled, but that doesn't necessarily mean the cylinder will only accept the homeowner's intended key combination.
And here's my concern: those remaining master pins may no longer serve any useful purpose.
Could Another Key Still Open Your Front Door?
Technically, yes.
If another key happens to have a combination of cuts that aligns with the available shear lines, it may operate the cylinder.
That doesn't mean your neighbour actually has a working key, and the likelihood of someone accidentally possessing such a key is small. But the possibility exists.
Every conventional mechanical lock has a limited number of usable key combinations. Key profiles, available cutting depths and manufacturing restrictions all influence how many different combinations are possible.
Even an ordinary lock without master pins cannot be guaranteed to have a completely unique key combination across Australia.
However, unnecessary master pins can increase the number of possible combinations that operate a particular cylinder.
And when multiple chambers contain those extra pins, the number of possible combinations can increase further.
The issue isn't that the original builder's key still works. It's that other, unintended key combinations may remain possible.
From my perspective, that's an avoidable security risk.
Why leave a lock capable of accepting unnecessary key combinations when those combinations can be eliminated?
What I Do When Rekeying These Locks
When a customer books me to rekey their home, I don't simply change the key combination until the old key stops working.
I also pay attention to what's happening inside the cylinder.
Construction-keyed locks are generally recognisable from their keying arrangements, identification markings and internal components. When I dismantle one, I can check whether unnecessary master pins remain.
If they do, I remove those redundant master pins wherever practical as part of my normal rekeying process.
The customer doesn't need to know what construction keying is, understand master pins or ask me to carry out this additional work.
It's already part of how I approach the job.
Removing these pins can involve extra work, and different locksmiths may approach rekeying differently. I can't speak for everyone in the industry, but I know the standard I want to maintain in my own work.
Some cylinders are more difficult to work on than others, and occasionally the design or condition of the hardware makes complete removal impractical.
But wherever reasonably possible, I prefer to leave the cylinder with only the keying arrangement it actually needs, rather than retaining unnecessary master pinning from the construction stage.
It's a detail most customers will never see, but it's part of the care I put into my work.
Should You Rekey a Brand-New Home?
It's worth considering, even if you're the very first owner.
If the construction-keying system has been correctly activated, the original builder's key should already be disabled.
But rekeying gives you the opportunity to establish a fresh key combination and remove unnecessary leftover master pinning where practical.
And construction keying isn't the only reason to consider rekeying a brand-new home.
Security screen doors and sliding doors are another area worth checking.
Some of these locks are supplied pre-keyed from a shared keyed-alike (KA) group, meaning multiple cylinders may be manufactured to operate with the same key combination.
That's convenient for suppliers and installers, but it also means the key supplied with your new screen or sliding door may not be unique to your home.
I've explained this issue in more detail in my article, Why You Should Rekey Sliding and Security Door Locks — Even in a Brand New Home.
There's also the convenience of having fewer keys.
Many newly built homes have one key for the front door and another for the security screen doors or sliding doors.
Depending on the brands and types of locks fitted, some of these may be able to be keyed alike, allowing several doors to operate with the same key.
Sometimes the whole house can use one key. In other cases, reducing the number of different keys to just two may be the most practical and economical solution.
So even if you've never had a previous owner, it's worth considering the security and convenience of your existing keying arrangements.
It's About Removing What Isn't Needed
Construction keying is a useful system. It makes life easier for builders and tradespeople, and it allows homeowners to take possession without immediately replacing their locks.
I have no objection to the concept.
My concern is what can remain inside certain cylinders after the construction key has been disabled.
If master pins are no longer needed, but still create additional possible operating combinations, why keep them?
When I'm already rekeying a lock, I believe those redundant pins should be removed wherever practical.
It's not something I expect a homeowner to know about, and it's not something they should need to specifically request.
It's simply part of how I believe a rekeying job should be done.
If you've recently moved into a new home, or you're considering changing your existing keys, you can learn more about my lock rekeying services in Geelong, Bellarine and Surf Coast.
A to Z Locksmiths — Geelong, Bellarine Peninsula and Surf Coast
Call or message Li on 0481 165 386 to discuss your locks.