It is a simple device that can detect a drop in blood oxygen level well before a person starts getting out of breath. If you are healthy, you should get a blood oxygen reading of 95 to 98. A pulse oximeter is capable of sensing the onset of hypoxia and, by far the best thing, painlessly. Historically, patients were measured by four vital signs: temperature, blood pressure, pulse and respiratory rate. When a finger is inserted in the pulse oximeter, it beams different wavelengths of light through the finger.

Source: The Telegraph June 21, 2020 09:11 UTC