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Solomon C. Nwaneri, PhD,  Department of Biomedical Engineering, University of Lagos.  E-mail: snwaneri@unilag.edu.ng A pulse oximeter is a medical device used to measure oxygen saturation (SpO2) in the blood. It is a non-invasive device. This means that the device does not penetrate or break into the skin. The blood needs a minimum amount of oxygen for the body to survive which is usually 95%. If the oxygen saturation is lower than the prescribed limits, a person is exposed to a condition referred to as hypoxemia .  Hypoxemia refers to oxygen levels that are lower than the normal saturation. This condition is characterized by shortness of breath and sometimes headache. Hypoxemia is usually caused by underlying diseases such as sleep apnea, lung diseases and several other possible causes. Oxygen should be in the haemoglobin of the blood known as oxyhaemoglobin(HbO2). Pulse oximeters operate based  on the absorption of different wavelengths of light. Usually, Red and infrared light are t