Short answer: yes, a stethoscope is totally helpful.
I worked for a locksmith, who taught me a bit about
safes. He had electronic stethoscope, which was
Christopher A. Young
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OT In the movies, safe-crackers are always listening to the tumblers
in the bank vault door. Sometimes they use a stethoscope.
Does that really work?
Decades ago I had a plastic toy safe, with transparent door and walls,
and it opened with a combination too. But there were no tumblers to
listen to. By turning a 2 full turns to the right and a little more
to the first number, then to the left a full turn and a little more to
the second number, and to the right to the 3rd number, the notches in
the rotating disks were aligned, and when the 3rd number was reached,
the third disk, which was a little bigger than the other two, allowed
the lock lever to move into all three notches at the same time.
Maybe I'm not clear here, but trust me, there were no intermediate
So if they can do that for a toy safe, worth no more than $5 now, why
wouldn't they do that for a bank vault?