Wire finders [1] are commonly used by electricians to find faults and repair wires without breaking our entire walls.

I am wondering if this can be a DIY project and if someone has worked on it. Specifically, the power injector component looks a bit tricky. Would anyone have played with it? I see that the tricky part would be to inject a low power signal into 120V power line wihout damaging anything. The signal has to be high frequency and low power to prevent appliance damage. Further, the overall circuit should be so designed that it does not get damaged when in touch with the power line.

[1] http://www.greenlee.com/products/WIRE-FINDER.html

 

If you using a coil that it can be receive the 50/60Hz signal and then using the op amp set it to a high gain to amplify the signal, and using led or Vmeter to show up the results.