A system and method for locating an object within a structure includes a magnetically-responsive member coupled to the object. A magnetic field generator generates a magnetic field in the presence of the structure. The generated magnetic field causes the magnetically-responsive member to output a signal when the magnetically-responsive member is in the presence of the magnetic field. A detector may include a sensor coupled to a control unit. The sensor detects the signal output by the magnetically-responsive member. The control unit locates the object based on detection of a third harmonic of the signal.