Chubb Detector Lock

Understand the basic lever lock before adding the clever part.

1. Pivot a flat lever with a slot cut in it, spring-loaded downward.
2. Fit a stump — a fixed post on the bolt — that sits in the slot.
3. The bolt can only slide when the slot's gate aligns with the stump.

Security comes from requiring several correct heights at once.

1. Stack several levers on the same pivot, each with its gate at a different height.
2. Cut a key with a different step for each lever.
3. Confirm the bolt only moves when every gate lines up together.

The invention itself: a trap for the overlift.

1. Add a spring-loaded catch positioned ABOVE the levers' correct height.
2. Any lever lifted past its gate is caught and held by that catch.
3. With a lever held high, no combination of lifts can align all the gates.

Attack your own lock and then recover it.

1. Deliberately overlift one lever and feel the detector catch.
2. Try the correct key — it should refuse.
3. Turn the correct key BACKWARDS to release the detector, then open normally.

Jeremiah Chubb patented the detector lock in 1818, reportedly prompted by a government competition following a burglary in Portsmouth Dockyard. The famous story is that a convicted locksmith held aboard a prison hulk was offered a pardon and a reward if he could open one, and gave up after months of trying. It appears in Chubb company literature and should be enjoyed with the usual caution about advertisements that become history.

The era of unpickable locks ended publicly in 1851. At the Great Exhibition in London, the American locksmith Alfred Charles Hobbs picked the Chubb detector lock, and then — over some fifty hours spread across weeks — opened the Bramah lock that had sat in a shop window under a 200-guinea challenge for decades. The lock trade was shaken badly, and there followed a genuine public argument about whether discussing lock weaknesses helped burglars or forced improvement.

Hobbs's answer to that argument is still quoted in security work: rogues already know these methods, and keeping the public ignorant only leaves them defenceless. It is essentially the case for full disclosure of vulnerabilities, made in 1853, and it remains the same argument.

What survives: lever locks are still standard on safes and on British door locks. The detector idea survives more widely as the principle that a security system should record and report attacks, not merely absorb them.