The present invention discloses a stud sensor, which is used for detecting the object hidden behind a surface, including a first capacitor plate, a second capacitor plate, a first detection circuit coupled to the first capacitor plate, a second detection circuit coupled to the second capacitor plate and a micro control unit. The first detection circuit processes the voltage signal corresponding to the first capacitance of the first capacitor plate and outputs a first voltage signal to the micro control unit. The second detection circuit processes the voltage signal corresponding to the second capacitance of the second capacitor plate and outputs a second voltage signal to the micro control unit. The micro control unit compares the first voltage signal and the second voltage signal to determine the position information including the central position of the object. The stud sensor of the invention also includes an output module to show the position information of the object, an input module to input instructions to the micro control unit. The invention has the properties of small size, high integration, fast response speed, high precision and good anti-interference.