I know the duress switch, as applied to safe and vault combination locks, has been around for some time. The idea is that a “slightly wrong” combination can be used to open a lock that also causes an alarm. But I don’t know about the history. So, a multi-part question –
When were the first duress-switch locks developed, and by whom? I assume some time after electricity and alarms became common, perhaps the early 1900s. Does anybody know of any patents?
Were there ever any non-electric analogs? For example dialing the duress combo causes a small flag to pop up near the ceiling (presumably in a way the bad guy won’t notice)?
Were there (are there) any examples outside of combination locks? I can imagine a key lock that opens in either direction but alarms if operated in the “wrong” direction. An example that came to my attention today is a fingerprint-reader that can be set up to open via two different fingers, but one of them triggers an alarm.
