A 3D localization system using magnetic field gradients that can replace X-Ray fluoroscopy in high precision surgery has been developed by our team. Monotonically varying magnetic fields encode spatial points uniquely in the field-of-view and are sensed by miniaturized devices with wireless power and data telemetry. Relative device locations are displayed in real-time. A prototype system consisting of a 65nm CMOS chip and gradient coils achieves a localization error of <100µm in 3D when tested in-vitro.