A smart compass sensor has been developed in standard CMOS with integrated signal conditioning and interface electronics. The compass sensors measure the horizontal components of the earth's magnetic field, which has a typical field strength of 25¿T. The sensor's offset is 4¿T (3¿), and its offset stability is less than 0.25¿T/week. Due to this low offset stability, the detection level is only limited by system noise. By using an improved chopper amplifier in the front-end the system noise has been reduced to 0.12¿T/¿Hz. In order to measure all three components of the earth's magnetic field, each sensor is packaged in a custom SFN8 package, which enables the necessary orthogonal alignment of three sensors. The presented 3D sensor module consists of three daisy-chained sensors, and illustrates the ease-of-use of a smart sensor with integrated bus (SPI/¿wire) interface. Apart from a single decoupling capacitor, no external components are necessary to read out the sensor signals, which reduces system costs.@en