Can it be used to trace 12/2 electrical wiring behind walls and in ceilings.

They say this tool is not designed to be used on any AC/DC circuits. But you can just make sure the electricity is turned of to the circuit and or wires you are trying to trace. The specs also say this tool has a good range, I find the range to be so so. I also found that the range depended on the type of wire you are tracing as I believe this is due to the insulation on and around the wire/wires. Romex wire I would generally get good signals because this is a solid core wire, this is why I believe it gives off a good signal.

This kit is able to detect behind drywall but likely will not detect in ceilings unless there is thin material similar to the drywall.