Chubb detector locks · explained · Manchester
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- Reset £40-70
- Key cut to the lock £25-55
- Do not force it
- 30-60 min
If your old lock has suddenly stopped working and the key now will not turn at all, and it is a Chubb, do not assume it has failed. It may have done precisely the thing it was invented to do, in 1818, and be waiting for you to reset it.
What the detector actually is
A lever lock works by lifting each lever to exactly the right height. The right key does that. A picker lifts them one at a time and feels for the one that binds, which means at some point they will lift a lever too far. So will a badly cut copy, and so will a worn key.
Jeremiah Chubb's idea was simple and rather elegant: put a mechanism in that notices an overlift. If any lever goes higher than the correct key ever takes it, the detector trips, the bolt locks solid, and the lock stops working for everyone including you.
That is not a fault. That is the alarm. The lock is telling you, however many decades later, that somebody had a go at it, or that a key has been cut badly.
Resetting it
On most detector locks, the reset is to turn the correct key in the locking direction, further than you normally would, which drops the detector and frees the mechanism. Then it works again as if nothing happened.
The problems: it needs the correct key, which is often the thing you do not have; the direction and feel vary between models and centuries; and forcing it while the detector is tripped is how the key snaps. If it will not go with light pressure, stop.
Why it tripped
Somebody tried it
Rare, but it is the reason the thing exists. Worth knowing about your own front door.
A badly cut copy
The usual culprit. A copy of a copy, cut a fraction high, overlifts a lever and trips it. See key cutting.
A worn original
A hundred-year-old key wears unevenly. Eventually one cut is wrong enough.
Dirt
A lever that sticks half-lifted and then jumps can trip it just as well as a pick.
What we do
Reset it, then find out why. If the answer is a bad copy, we cut a fresh key to the lock rather than copying the bad one, because copying it just trips the detector again next month. If the answer is a century of dirt, we strip and service it.
We do not replace these unless we have to. A Chubb detector lever lock is usually better made than anything you can buy today, and it is in a door that was cut for it. See mortice locks.
What it costs
| Job | Price |
|---|---|
| Detector reset | £40-70 |
| Reset plus strip and service | £60-100 |
| Key cut to the lock (not copied) | £25-55 |
| Opened, no key at all | £65-130 |
| Replaced with BS3621, if it must be | £85-140 |
Broken key extraction · BS3621 explained
Questions people actually ask
What is a Chubb detector lock?
A lever mortice lock with a mechanism that notices when a lever is lifted higher than the correct key ever lifts it. Jeremiah Chubb patented the idea in 1818 and it is genuinely clever: a picker works by lifting levers one at a time and feeling for the one that binds, so sooner or later they overlift one. When that happens the detector trips, the bolt locks solid, and the lock stops working for everybody, including you. It is not a fault, it is the alarm going off.
My Chubb lock has stopped working completely. Is it broken?
Possibly not. If the key suddenly will not turn at all in a lock that was fine yesterday, the detector may have tripped, which is the lock doing exactly what it was designed to do. On most detector locks the reset is to turn the correct key in the locking direction, further than you normally would, which drops the detector and frees the mechanism. If it will not go with light pressure, stop, because forcing it while the detector is tripped is precisely how the key snaps.
Why would the detector trip if nobody tried to break in?
Usually a badly cut key, and that is the most common cause by a long way. A copy of a copy, cut a fraction too high, overlifts a lever and trips the detector exactly as a pick would. A worn hundred-year-old original does the same eventually, because it wears unevenly until one cut is wrong enough. Dirt can do it too: a lever that sticks half-lifted and then jumps looks identical to the detector. Resetting it is £40 to £70, but if the cause is a bad key it will trip again next month unless the key is fixed.
Should I replace my Chubb detector lock with a modern one?
Only if you have to. These are usually better made than anything you can buy today, and they sit in a door that was cut specifically for them. We reset, service and cut keys to them rather than replacing them. The one genuine reason to replace is if your insurer requires BS3621 and yours predates the standard, which many do, in which case it is £85 to £140 fitted. Otherwise, keep it.