A pulse oximeter is a device that checks to see how much oxygen your blood is carrying.
Usually a small clip is put on the end of your finger. (Sometimes it's put on your toe or earlobe.) The device shines a light beam through the skin. It estimates your oxygen level by measuring the percentage of your blood that's carrying oxygen. Your oxygen level (or oxygen saturation, SpO2) shows on the display screen.
Pulse oximeters are used in doctors' offices and hospitals. Some people use one at home. This may be the case for people who have a condition that affects their oxygen levels. Examples include people who have long-term heart or lung problems or an infection like COVID-19. If you use an oximeter at home, be sure you know how to use it correctly. Ask your doctor what to do if you see your oxygen level change over time.