This work presents two handheld instruments built at our laboratory able to detect sub-surface cracks in a plate of conductive material. Both instruments contain a probe composed of an excitation coil and a giant magnetoresistance sensor (GMR) acting as the magnetic field sensor and includes a computer mouse pointer as positioning system. This configuration, despite its low cost, allows better performances in the detection of sub-surface defects than commercial equipments. Deeper defects in the material can be detected due not only to the high sensitivity of the GMR sensor, which is constant in a very large frequency range (10 Hz – 1 MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system.