How do smart watches measure heart rate?

The smart watch measures the heart rate through the LED light emitted from the back of the case through the reflected light generated by the blood on the wrist when the blood flow of blood vessels. For example, when the heart contracts, the heme in the blood will become dense and the green light is reflected back less. At this time, the watch records that the heart contraction; when the heart relaxes, the watch records more green light, the heart diastolic, and then records the number of times the heart diastolic and contraction per minute to get the current heart rate.

I. How do smart watches measure heart rate?

1. Smart watches usually use an optical method to measure heart rate, that is, to calculate the change of heart rate through the effect of LED light emitted behind the case on the wrist. There will be heme in the human blood, which absorbs green light and reflects red light. When the heart is diastolic and contracted, the blood red density is different, then the emission effect on green light is different.
2. If the heart relaxes, the heme density in the blood will decrease. At this time, the effect of absorbing green light will be worse, and the watch will collect more reflected green light, so it will judge that the human heart has relaxed once.
3. If the heart shrinks, the heme density in the blood will increase. At this time, the effect of absorbing green light will be stronger, and the watch will be less green light reflected back, then it will judge that the human heart has been collected once.
4. By continuously emitting LED light within a minute and then transmitting it on the blood vessels of the wrist, we can get the total number of heart diastolic and contraction in a minute. Finally, you can know the heart rate value of the person at that time, which is the principle of measurement.
5. Does the smart watch measure the heart rate accurately?
   The accuracy can generally exceed 90%, which is generally accurate, but it will be affected by some factors, such as the location of the watch, the system of the watch, etc. If you want to be more accurate, don’t hold the watch close to your wrist. There are some gaps in the middle to prevent the restriction of blood circulation at the wrist, and then do not wear the wrist bone or place with tattoos.
6. Is the heart rate of smart watch harmful to the body?
   No. The LED light emitted by the smart watch when measuring the heart rate is radiation-free and does not cause harm to human health. Therefore, there is no need to worry that the watch always measures the heart rate and affects people’s health. On the contrary, it can also have a good monitoring effect on health.