You should always be sure that its safe to drill before doing so and with the bosch pmd 7 youre able to do exactly that this useful detector helps to locate live electrical cables as well as ferrous metals such as steel framework and non ferrous metals such as copper piping all bosch detectors have automatic calibration and only calibrate once the device is set up against the wall this avoids the traditional error of calibrating it before placing it against the wall and the detector then