How did Jeremiah Chubb’s detector lock reveal tampering?

Jeremiah Chubb’s detector lock revealed tampering through the use of a specialized internal mechanism called a detector. This component consisted of a retaining spring designed to catch and hold any tumbler that was raised too high during an unauthorized attempt to pick the lock.12

When a tumbler was lifted beyond its correct height by an inexpert hand, the detector spring would engage, effectively locking the mechanism and rendering the bolt immovable. This action served a dual purpose: it prevented the lock from being opened and provided visible evidence that the device had been tampered with.12