squelchtone wrote:I'm not sure what locksmiths do in the field to prevent that from happening, but as far has hobby lock picking goes, this is one of the reasons we tend to scold new pickers for picking their home, apartment and dorm locks, because things can and do go wrong, especially when in a master keyed environment.
Personally speaking whenever I had to adopt an orphaned master keying system whenever my long-time-ago former employer acquired a new building via purchase or management contract, I would always make a set of "try out keys" from the master key... Sort of a reverse process of what Matt Blaze described in his Rights Amplification paper...
"M" = known cut from TMK
"X" = cut space being explored
M M M M M X
M M M M X M
M M M X M M
M M X M M M
M X M M M M
X M M M M M
You would only need a set of 24 try out keys on most 6-pin two-step progression keying systems using 10 bitting depths...
During the transition/turnover phase before a new keying system would be installed the "try out keys" would allow you to determine what change key bittings the lock was keyed to without taking it apart... Lots of keying systems die an early death because nobody keeps proper records or maintains a key box with an example/reference copy of every key in the system so that duplicates can be made by technicians with no specific lock experience... Once you have lost a reference copy of a specific change key you either need master keying skills to use "try out keys" to determine the change key bitting again or you need to have that lock serviced by a locksmith...
Those "try out keys" were also useful in the case of maison keyed or cross keyed cylinders that lost a mater pin -- no picking required to open the locks as one of the "try out keys" will open it as long as the only problem is that a pin has escaped... Assuming of course that whomever created the system followed the rules and used the proper progression -- i.e, "try out keys" would not work on an ad hoc or "shoebox" type master keying system or do anything at all with SKD keyed cylinders...