According to the WHO, 15,000 children under five years are dying every day from preventable causes with 80% of these children being born in low-income countries. Portable optical medical diagnostic devices can help physicians, nurses and untrained health workers to objectively identify children who are at a higher risk of dying. In the last 2 years, we collected the oxygenation values of the brachioradialis muscle, using a commercial Near Infrared Spectroscopy (NIRS) device, in 200 children under 5 years admitted in two hospitals in Uganda. Data revealed that the tissue oxygen saturation decrease during a vascular occlusion predicts children at higher risk better than other vital signs (SpO2, respiration rate, heart rate and temperature). Based on these results, we designed a low cost Continuous Wave Spatially Resolved NIRS device controlled by a smartphone in order to extend our study to a larger population and confirm our observation. The total cost of this device (excluding the smartphone) is less than $100. The preliminary tests suggest a significant potential of our low cost mobile NIRS device and oxygenation values closely matching those reported by the best device on the market.