How does Pulse oximeter work? Pulse oximetry is a non-invasive and painless test that measures your oxygen saturation level, or the oxygen levels in your blood. During a pulse oximetry reading, a small clamp-like device is placed on a finger, earlobe, or toe. Small beams of light pass through the blood in the finger, measuring the amount of oxygen. It does this by measuring changes of light absorption in oxygenated or deoxygenated blood. This is a painless process. The pulse oximeter will thus b