From my research, I know that Apple Watch measures heart rate using a method called plethysmography. During active measurements, the green LED light is activated. However, I read somewhere that Apple Watch can also measure PASSIVELY heart rate WITHOUT the green LED light being activated by using infrared light. Is this true?
Are there other devices, like Fitbit Alta HR, that can measure heart rate PASSIVELY without having the bright green LED light on?
Are there other devices, like Fitbit Alta HR, that can measure heart rate PASSIVELY without having the bright green LED light on?