A reflective SpO2 measurement system includes a light source that emits light of at least a first and second wavelengths, and one or more detection devices forming a close detector positioned at a first distance from the light source and a far detector positioned at a second distance from the light source, wherein the second distance is greater than the first. The SpO2 measurement system is configured to operate in a high power mode to determine a calibration factor based on the comparison of light reflections detected by the close detector and the far detector. The system is further configured to operate in a low power mode to generate a low intensity light pulse, and detect a close reflection of the low intensity light pulse with the close detector. An SpO2 is then determined based on the close reflection of the low intensity light pulse and the calibration factor.