According to the search Xiaomi bracelet 6 this time the new addition of blood oxygen detection function, the data is only for reference and not medical grade, so it does not claim to be a class II medical device.
Class II medical devices include thermometers, sphygmomanometers, cardiac diagnostic instruments, medical cotton wool, medical gauze, constant temperature incubators, glass cupping device, X-ray film machine, ultrasound, microscope, biochemical instrument and so on.