First, install the heart rate measurement software on the iPhone, put the index finger on the camera behind the phone, cover the flash, and the software can start working.
It should be noted that the heart rate should be measured at rest as much as possible. The sudden change of external ambient light and finger movement will lead to large deviation of measurement results.
If the software is allowed to access the "Health" that comes with the system, the measured data will be synchronized to "Apple Health", and then you can see the heart rate data in "Health".
Do you know how the camera measures the heart rate? When the heart beats, it pumps new blood into the capillaries. Because of the high oxygen content in fresh blood, the color of blood will change slightly. The color change of blood can be monitored by continuously illuminating the subcutaneous capillaries of fingertips with a flash lamp, and the heart rate can be calculated from the periodic changes.