I have to drill a 2 1/2 inch hole through an exterior wall, and I know that
it is possible that I could run into wiring. While I know that I could
turn this circuit off and drill away, I can envision that it would be hard
to access both ends of the 120 volt wiring if my drill should cut a wire.
(repairing would normally be easy, but I don't know if I would have
appropriate "slack" and/or if I could get to both ends to do the repair. )

Isn't there a gadget to allow one to locate the exact wiring location in a
wall ?

Thanks for any tips !!

James