How Heart Rate Sensor Works in Fitness Band - Photoplethysmography | Heart Rate Monitor

How do fitness watches and smartwatches like the Apple Watch, Fitbit, and Biostrap measure heart rate and heart rate variability?
How do Smartwatches measure heart rate?
Why do Apple Watch and Fitbit have a green light on the back?
What are the green lights on the back of an Apple watch?

Fitness trackers like the Apple Watch, Fitbit, and Biostrap measure heart rate (heart rate monitor) and other health data using Photoplethysmography or PPG technology.

Photoplethysmography works via an optical sensor in your watch that shoots either a red or green light onto the surface of your skin.

When this light reaches your blood vessels, some is reflected to a photodetector on your watch. The intensity of light reflected back captures a waveform of the amount of blood in your blood vessel.

Who Uses What:
Apple Watch green light and
Fitbit blaze green light PPG
However, Biostrap red light PPG is used to measure clinically accurate advanced biometrics like heart rate variability and oxygen saturation.

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Doctor Yogendra
- Board-certified Physician Anesthesiologist and Medical Researcher