Locating CAT3 wire with Transmitter and Receiver
Well, if they are wired as for phone wiring still, they would all be tied together. 

If you have undone that wiring already, they may be having "cross talk" from the RF signal getting picked up by adjacent wires - CAT3 is not as good at rejecting this as CAT5, 6 or 7. You might be able to note a change in volume of the "beep" in that case, but really, if you are not hunting for wires behind the wall, you're  probably using the wrong tool. 

I'd pull out either a pair tester (since I own a couple, as a "network guy" - they are pretty cheap) and plug it in, where you will either see lights or not, depending on a DC connection that's not subject to crosstalk...

...Or else grab a simple meter (volt or ohm) and either attach a 9V battery to a certain pair and look for voltage, or short a certain pair and look for low-ohms (or continuity) - this might require hacking up a patch cable to make the connections.

Here's a simple, cheap pair tester (under $10 - similar to what I have but mine are too old to have examples for sale now - no affiliation)


You can find things with the same name that cost a lot more, as they add fancier functions you don't need for the simple tests.