The beeper function on your meter probably beeps whenever anything lower
than 30 ohms or so is across the test leads. This level may vary from one
make of meter to another, but it's a starting point.
BTW -- I learned this the hard way: Don't depend on the beeper!!! If you're
trying to find out of something is shorted, or trying to "ring out" a cable
harness (that is to say, locate a particular wire among a bunch of others),
or checking a fuse, it's tempting to listen to the beeper only and not look
at the meter's display. Don't do this!!!! I once had a weak fuse give me
trouble this way... instead of opening, it was dying of old age and had
increased its resistance just enough to "eat up" all the current going
through it and cause trouble downstream. But because I was checking the
fuse "by ear," I didn't realize this. Since the meter was still beeping, I
assumed that the fuse was good. But it wasn't! From that point on, I
always look at the numeric display and see what it says instead.