I'm doing some work in my attic to upgrade insulation. I'm pulling up the existing insulation as I go to ensure that there are no problems. I'm coming across alot of old knob and tube wiring, alot of which has been disconnected, and new wiring has been run all over. There are a few places where the wiring disappears down through the ceiling. I'm guessing that these wires are no longer live, but I want to be sure before I add new insulation. What's the best / easiest way to test these old wire to ensure they have been disconnected? I plan on removing any old wiring I find to leave no doubt for the next guy that owns this 80 year old ramshackle. Can I trust a non-contact voltage detector?