This article describes an alternative to high-field electromagnetic tracking system, by using low consumption generator and high-performance magnetic sensors. Monotonically varying magnetic fields over three positions are created to produce magnetic field gradients, which encode each spatial point uniquely. Millimetric size sensors capable of measuring their local magnetic field with high resolution are used to sense the gradient field. Such sensors can be embedded in surgical tools, such as catheters or brain electrodes. With a low power consumption and low-field generator, the integrability of the electromagnetic system in a surgical theater is greatly enhanced. This system leads to unambiguous and orientation-independent spatial encoding with a mean absolute error of 3 mm at 42 cm from the field generator using the last generation 3-D axis magnetoresistive sensors. A calibration of the sensors was performed and leads to significant improvement in the localization over the Z -axis.