Burned $85 on a cheap toner probe kit from a supply house in Tulsa and it nearly cost me a whole panel job
I grabbed a no-name tone and probe set from a supply house in Tulsa for $85 to trace some buried zone wires in a 1970s ranch house, and the thing couldn't pick up a signal through a foot of drywall. It left me guessing on which pair went to the front door contact, so I almost wired the wrong zone and had to pull the whole panel back open. Anybody got a probe that actually holds a tone through old plaster walls without making me question my whole career?
Ran into the same thing with old plaster, the trick for me was ditching the alligator clips and using a good set of test leads with a ground reference on the panel can. Also try turning the receiver gain way up and sweeping slow, like an inch a second, because those buried wires in plaster go dead in spots. Cheap kits just don't push enough signal for the lath and horsehair walls, so you're not crazy, the tool is.