A pulse oximeter – pulse oxygen meter – measures the amount of oxygen in your blood in a non intrusive way. No needles are required and a blood sample does not need to be taken. It works by passing a beam of light through your finger using a finger attachment (try looking at a bulb through your finger – some of the light will pass through).
The oximeter passes through beams of light of wavelengths 650 nm and 900 nm respectively. Absorption of light is different for each wavelength. Absorption depends on how much oxygen in absorbed by the haemoglobin in your blood cells. If more oxygen is absorbed, the blood appears more red.
The absorption of light after pass through the finger is detected and analysed by a computer. An absorption raise of ;less than 95% is cause for concern.