I bought a Southwire M400TP Cable Mapper a few years ago and then discovered that it also had a tone generator. I ordered this sensor along with it and it has been one of the most useful tools I have purchased to date. I've lost count of the number of times I've gone to a site to install a PC or PIN, only to find that someone messed with the wiring and none of the connectors or cables are properly labeled. I just plug the M400TP into the jack on one end and use a wire probe on the other end. Once I've found the right cable, I can connect the remote control from the M400TP and test the cable.