In this paper three different eddy current testing (ECT) based methods are used to detect and evaluate the depth of cracks in conductive surfaces. Although having the same goal, the methods use different approaches to solve the problem of estimating defect depths. The first method uses the conventional eddy current testing method that applies a sinusoidal current in a circular coil embedded in the probe which includes a giant magneto-resistor (GMR) to measure the magnetic field density. In the second method the probe includes a planar coil as excitation to provide an area with uniform current distribution and a GMR as magnetic sensor. The third method is based on velocity inducted eddy currents with a moving probe that contains a permanent magnet and a Hall effect sensor to measure the magnetic field. This paper includes a detailed description of each implementation and a comparison of the results obtained by each method.