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Message: <blockquote data-quote="imhotep" data-source="post: 25658014" data-attributes="member: 562115">The readings from these so called "wearables" are not really accurate but enough for non medical use. The principle behind this is PPG (photoplethysmography) - basically light and a photodetector.  When the light emitted by the LED enters the skin, most of it is absorbed but some of it is reflected back. The amount reflected depends on the volume of the arteries near the skin surface. Blood pulsing in the artery causes the reflected light to change up and down and this is processed to estimate the heart rate.The accuracy depends on the quality of the product. Apple Watch 4 and Garmin Vivosmart 4 are supposedly the best and consitent among the consumer grade devices.</blockquote>

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