Non-invasive assessment of arterial oxygen saturation has traditionally been entrusted to pulse oximetry. Whereas commercial probes are confined to the finger tip or the forehead, several recent works aim at enlarging the range of placement sites. In the context of the development of a continuous multi-parameter health monitoring system, CSEM is exploring the reliability of pulse oximetry measurements at the sternum. This talk will address both theoretical and practical aspects of the development of such a sensor with special emphasis on the reliability of the measurement. Experimental data obtained from a novel eight channels sensor will be presented.