Oximeter, also known as pulse oximeter, measures the oxygen content of human blood, i.e. blood oxygen saturation. Normal people's blood oxygen saturation between 94%-100%, below 90% need to pay attention. If the blood oxygen index is below 90% after infection of a new crown, it is likely to develop into severe pneumonia and requires prompt medical attention. Some of the elderly due to poor immune response, infection does not appear after the symptoms or symptoms are mild, showing "silent hypoxia" symptoms, also need regular monitoring.