Here is a brief overview of how a pulse oximeter works. A pulse oximeter has two LEDs, one red and one infrared, and a sensor contained in a finger clip. The LEDs shine light through the finger which will absorb the light from the two LEDs. There will be varying amounts of absorption based on the amount of blood oxygenation that is occurring. Typically, the richer the oxygen content in the blood, the redder it’s going to be and the sensor will be able to detect this.