The heart rate sensor measures your heart rate in Beats per Minute using an optical LED light source and an LED light sensor. The light shines through your skin, and the sensor measures the amount of light that reflects back. The light reflections will vary as blood pulses under your skin past the light. The variations in the light reflections are interpreted as heartbeats.and surprisingly it's quite accurate....same mechanical to measure oxygen saturation...good saturation of oxygen absorbs more ir light ...bad oxygen saturation absorb more red light so rgb setup of ir and r accurately measure oxygen levels also ...only you can't measure blood pressure as it need sphygmomanometer and stethoscope
I have compared our spo2 values with a proper spo2 measuring devices used in a hospital. I would say our mobile are pretty much accurate but I wouldn't replace it with the clinical spo2 measuring device. rest is well explained by @interchupipi
