Extech’s RT30 Wireless AC Circuit Identifier ($145) feels like a quality tool when you pick it up, and it proves its quality when you use it. I use mine for two things. The first is to trace electrical circuits in mid-run. This is a nice feature if you have open walls, a crawl space or an attic space where you have access to your electrical cable. To test the wiring, you either clamp the sender unit directly to the wiring or use the included clamp probe to attach it to the cable. Once you have the sender unit, or probe, clamped in place and sending a signal to the receiver unit, you go to the circuit panel and flip off the breakers until the receiver unit no longer receives the signal from the sender unit. Then you’ve identified your circuit. I also use the Circuit Identifier to determine which circuit outlets or recessed lights are on by using a light sensor on the sender unit. You simply plug a lamp into the outlet and turn it on. Or turn on the recessed lights. Then place the sender unit close to the lamp or the lights so the sender can detect the light. After the sender signals the receiver, you identify the circuit by flipping circuit breakers until the receiver stops receiving the signal. The tool is perfect for finding the circuits for those mystery wires in an attic or crawl space. It’s also ideal for people like me who work alone trying to trace wiring—I don’t need my wife to stand in an adjacent room yelling, “On! Off!” Overall, I find this a useful tool that’s easy to use for the weekend warrior. My only complaint: I wish there was a better way to trace electrical outlets than carrying a light around the house with me to plug in. Retailers for the Circuit Identifier are listed on the company’s Web site. Extech, (781) 890-7440, ext. 220. extech.com --Steve Schilling, field editor