Nowadays, smart wearable devices can monitor the heart rate, however, this data is not accurate, there is an error, the reason for this error how to cause? That starts with the principle of heart rate monitoring. Most of them use optical sensors, through the LED lights to illuminate the capillaries on the wrist, the sensor through the blood flow rate to calculate the heart rate, but this principle is susceptible to light, sweat, tattoos, so it causes errors.Suunto heart rate belt (orange) and Basis Peak (blue) heart rate data comparison (image from Tencent) foreign media tested a few models of the monitoring of the heart rate of the smart wearable devices and compared the data with that obtained from two heart rate bands, Polar V800 and Suunto Ambit3. The testers jogged wearing the watch and the heart rate bands and then made the final comparison. The final comparison showed that the Garmin Forerunner 225 had an error rate of about 10% in the middle of the run, when the heart rate was gradually leveling off, the Adidas miCoach sports watch had an accuracy rate of about 86% and an error rate of 14%, and the Basis Peak averaged an error rate of 25%.