Optical pulse sensing
Many wrist wearables use photoplethysmography (PPG): light is directed into the skin and changes in reflected light are used to estimate pulse-related signals. Motion, fit, and skin contact can influence signal quality.
Motion and context
Accelerometers and gyroscopes detect movement. Together with pulse-related data, they can support estimates about activity, sleep, and training patterns.
Algorithms turn inputs into summaries
Heart rate, sleep stages, calories, readiness, and similar outputs may be calculated from sensor inputs. They are modelled estimates, not direct measurements of every underlying bodily process.
A note on health information
This article is for general education, not medical advice. GRND is not a medical device. For symptoms, diagnosis, treatment, or urgent concerns, contact a qualified healthcare professional or local emergency service.