I might be far-off on this, but I know there's testers that can 'feel' current running through wires, without actually touching the wires (that's how those inexpensive X-mas bulb testers work). In theory, you could follow the wires, using this type of tester, until you found where the break was. It may take some work, especially if there's more than one circuit running through EMT, but this would certainly prevent you from breaking into walls at random spots.
I think I've seen these testers at home improvement stores (Menards, Home Depot, Lowes, etc). Hope this helps.