A hand-held power drill incorporates an electronic voltage sensor having a sensing input conductively connected to the drill chuck so that a drill bit held by the chuck serves as a voltage sensing element. The electronic voltage sensor can operate an audible or visible warning device, and can also disable the drill motor, when the drill bit is in close proximity to a live wire. A two pole switch with successively closed sets of contacts allows the drill to be used as a voltage probe without operating the drill motor. An auxiliary by-pass switch gives the operator the option to operate the drill even when it is in proximity to a live wire.