A fluxgate magnetometer suitable for contactless reading of extremely weak sources such as documents in magnetic ink, has been developed using planar microtechnology. It is shown that the sensor can be miniaturized using a flat shape of core, which does not need to be surrounded by windings. A one-layer pick-up coil which is easy to fabricate is positioned on top of the core. In batch processing using permalloy films, the sensors can be made all alike. This is important for the compensation of the earth's field by means of two sensors. © 1990.