Frank B Denman writes:
I've got a Sperry CS-500A that is essentially useless. It is never able
to narrow its detection to a single breaker.

I've got one purchased from Home Depot for about half that amount; can't
remember the brand at the moment. It seems to be able to narrow the
breaker down to one of 2 or 3 on its own, particularly if you rotate the
pickup head to its most sensitive position (either parallel or
perpendicular to the breaker, again can't remember which).

Once you've narrowed it down that far, you just turn off one breaker and
see if the audio signal goes away entirely. If so, you've found the
correct breaker. (The tone generator is powered by the outlet it is
plugged into, and produces a pulsing audio note - it's very obvious when
it goes away even in the presence of other noise).

If the tone continues, try the next closest breaker till you find the
right one. This does have the disadvantage of occasionally turning off
the wrong circuit for a few seconds, but it's a lot better than going
through the whole panel trying each breaker. And it doesn't require an
assistant to tell you when the circuit goes off.

Dave