I understand that Apple Watch detects heart rate this way

Before Apple Watch actually reached consumers, Apple first released a new support page for Apple Watch, which details the device's heart rate monitor. As we all know, the heart rate monitor equipped with Apple Watch will measure the intensity of the user's exercise during exercise.

Combined with heart rate, a data that can show exercise intensity, Apple Watch can more accurately measure the amount of calories burned by users every day. In addition, users can also use the heart rate Glance function to check their own heart rate anytime, anywhere. However, in addition to these two functions that users will use, the new support document also details the technology behind the hardware and some little-known software features.

According to the document, the Apple Watch will quietly measure your heart rate in the background every ten minutes. This data will be stored in the iOS 8 "Health" app for later viewing and integrated with third-party health tracking apps and hardware.

In addition to software, Apple said that Apple Watch also uses very good technology to achieve heart rate collection:

The Apple Watch's heart rate sensor uses a technique called photoplethysmography to collect heart rate data. The technology is based on a very simple principle: blood is red because it reflects red light and absorbs green light. Therefore, the Apple Watch uses green LEDs paired with light-sensitive photodiodes to detect the amount of blood flowing through the wrist at any given moment. When the user's heart beats, more blood flows through the user's wrist, and more green light is absorbed. Between heartbeats, blood flow decreases, resulting in less absorption of green light. By flashing the LED hundreds of times per second, the Apple Watch can calculate the number of heart beats per minute - that is, the heart rate.

In addition to using green LED lights, the heart rate sensor also uses infrared to monitor the user's heart rate. Infrared mode is the method used by Apple Watch to measure heart rate every 10 minutes. Apple Watch will only switch to green LED when the infrared system is not sufficient to provide accurate readings. In order to compensate for the heart rate signal and avoid the signal being too weak to affect the reading, Apple has increased the LED brightness and sampling rate of the heart rate sensor.

Like other wearable devices equipped with heart rate sensors, the heart rate sensor of Apple Watch is not perfect. Apple pointed out in the document that how users wear Apple Watch will directly affect the success rate of heart rate collection. In order to get the most accurate reading, Apple recommends wearing the device as close to the skin as possible.

Apple finally pointed out that the accuracy of heart rate measurement will be more accurate when users are doing rhythmic exercise (such as running and cycling) than irregular exercise (such as tennis and boxing).

As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity.