Mechanical locks normally require 4 digits and a single character in order for the lock to function. This normally excludes the “C” character as that is reserved for cancelling an input.
Here’s the catch, they don’t have to be pressed in any particular order! We only need to figure out which buttons are being pressed, not in which order they are pressed in.
So to do this we simply need some lemon juice and a black light. Smear some lemon juice onto the buttons on the key pad. Throughout the working day people will press the correct buttons continuously. As a result the lemon juice should be removed over time. Go back with the black light… hey presto… insta-breaking and entering.
These locks are also prone to a bypass if the rubber is missing/soft round the edging. A “slim jim spanner” (a very thin metal spanner) can be pried through the rubber surround to the bar controlling the lock. Since the mechanical lock does not actually stop the barrel turning, the lock can be jimmied open this way also.