I bought it because in the new type sockets with plastic cover, the classic tester cannot detect voltage in the internal holes for child protection. Of course, it will not replace it because it cannot screw in the power. Essentially, one complements the other and this one will show you the presence of voltage with two sensitivity levels, in loose cables left in the air by electricians (not all), or in active cables and sockets, with a faster sound in the phase and slower in the neutral. In high sensitivity, it can detect an active line inside the wall, but approximately, for example, while you see the line coming down vertically from the box to the socket, it also detects it 40 cm to the right and left without any sound variation, which I would not trust for a specific hole. Good quality construction, the flashlight is useful and reaches 20 meters. In conclusion, for its price, it is very good and a life saver. Of course, it is important to test the tool in a socket or cable that you know has electricity, as it is written in English in the instructions for the first use.