Pulse oximeters measure Oxygen Saturation (SpO2) or the oxygen levels in your blood. Having low levels of oxygen means your body is hypoxic and needs more.
During the current health crisis, monitoring ones blood oxygen levels can decide whether you stay at home or seek further care. With hypoxia, your heart rate can increase due to increased demand for oxygen around the body.
Pulse oximeters use light diodes to approximate your blood oxygen levels and can be used to monitor your oxygen levels while staying at home.