Nothing to do with VoIP, but security minded people might be interested in this.  At the Victoria & Albert Museum (V&A) in London, I saw this mechanical indicator lock:

This device has two counters integrated into the lock: one is a dummy, and the other counts the number of times that the lock has been opened, allowing you to carefully monitor access to your piles of gold, kidnapped princesses, battle plans, and other precious posessions.

It’s very easy to fall into the conceit of thinking that security is a modern concern, but devices like this have been around for centuries.