A pulse oximeter is a device or an app feature that is used to quickly and easily monitor a person's oxygen saturation and oxygen levels. This means it can measure the level of oxygen within the blood, especially arterial blood without using any invasive means. It also measures the oxygen saturation of pulsating blood, which is commonly known as SPO2. A person's heart rate is automatically calculated alongside the percentage of oxygen. The pulse oximeter uses light to work out the oxygen saturation. Light is emitted from the light source, which goes across the pulse oximeter probe and reaches the light detector. The light passes through the skin to reach the detection needed to accurately rate the oxygen levels in the blood. This reading is then conveyed on the pulse oximeter in the form of a percentage.