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Oxygenated blood absorbs light preferentially at 940nm (near infra-red light), whereas deoxygenated blood absorbs light preferentially at 660nm(red light). A pulse oximeter works by passing a beam of red and infra-red light through a pulsating capillary bed and then measures the amount of red and infra-red light emerging from the tissues via sensor. The relative absorption of light by oxyhemoglobin (HbO) and deoxyhemoglobin is then processed according to the Beer-Lambert’s law and the oxygen saturation level (SpO2) determined. For Home, Hospital, Sports or Aviation use.