A pulse oximeter is a medical device used to measure the oxygen saturation level in a person's blood, as well as their heart rate. It is a small, portable device that typically clips onto a person's finger, although other parts of the body such as the earlobe or nose can also be used.

The device works by emitting two wavelengths of light, usually red and infrared, through the skin and into the blood vessels. Hemoglobin, the protein in blood that carries oxygen, absorbs these wavelengths differently depending on whether it is carrying oxygen or not. By analyzing the amount of light absorbed, the pulse oximeter can calculate the oxygen saturation level in the blood, expressed as a percentage.

Pulse oximeters are commonly used in medical settings such as hospitals, clinics, and emergency situations, but they are also available for home use. They are particularly useful for monitoring individuals with respiratory or cardiac conditions, such as chronic obstructive pulmonary disease (COPD), asthma, or heart failure. Additionally, they are frequently used during surgeries, in intensive care units, and by athletes to monitor their oxygen levels and heart rate during training and recovery.