In article ,
mm wrote:

Can one open a combination lock without knowing the combination?

I'm helping to clear out a building which is about to be torn down,
and in the office is a sheet metal cabinet, with a door on the left
side and two shelves inside, and on the right side is a larger door
with a safe-style lock on it, a single dial, a black plastic wheel
with numbers on it.

By no means is this worth the money that a professional would charge
-- we never even locked it when we were using the building, or we
would still remmeber the combination -- but it seems like a
challenging project to me.

It got locked somehow and no one remembers the combination. I've
heard that it is still possible to open them. That the movies are not
entirely wrong, with someone using a stethoscope to hear the
"tumblers" "fall" into place.

OTOH, I had a toy safe, when I was about 20 years old, twenty!, and it
was clear plastic inside, and I could see the gears turn when I turned
the dial on the front, and even in this toy, there were no tumblers to
fall as one or more of the three wheels (the gears) each with a notch
in one place, got their notches lined up. Only when all three notches
were lined up, could one open the plastic safe.

There was nothing to hear until the last second when it opened.
Rotating the knob and the gears made no special noise at any point
(except maybe a noise could be heard after one reversed direction of
the knob and when a cog on a gear close to the front hit a stop on the
next gear back and it started to turn. but what has the number that is
at the top of the dial at that moment got to do with the combination
number? Is that it? Can the latter be deduced from the former?) I
don't see how it could be.

From Wikipedia "Some rotary combination locks can be manipulated by
feel or sound in order to determine the combination required to open
the safe. More sophisticated locks use wheels made from lightweight
and soft materials such as nylon, which reduces this vulnerability."
This seems like nonsense. Why does it have to be "sophisticated" when
my 4 dollar plastic toy safe couldn't be opened by feel or sound?

One webpage says "Despite the tried-and-true design of the safe, it
contains a fundamental weakness: Every safe must be accessible to a
locksmith or other authority in the event of a malfunction or
lock-out. This weakness forms the basis of safecracking." It says
"every" but does that really apply to something that probably costs no
more than one or two hundred dollars new now.

BTW I don't think this is a fire safe or a real burglary safe. It
bangs too much to have fire insulation in it (and I saw it when it was
unlocked and open, come to think of it) and anyone could cut into it
with a hack saw, or a boy scout can opener, or puncture a hole with a
big screwdriver.

Sounds identical to a gadget we had to open after the boss died.
Locksmith wanted around three or four hundred dollars. After two weeks
of discussion, a couple of people just pried it open with a crowbar or
something. It's basically sheetmetal, as you noted.