The Xiaomi Smart Band 9 Pro uses an intelligent system to monitor your heart rate, and it has a feature designed to send reminders when your heart rate is too high or too low. However, the device does not trigger a reminder immediately when the heart rate exceeds the set threshold. Instead, it waits for a more consistent pattern, specifically if your heart rate remains above the high threshold or below the low threshold for at least 10 minutes while you're at rest.
This approach helps to avoid false alarms in cases where your heart rate can briefly exceed or dip below the threshold due to momentary activities like physical movements, sudden changes in posture, or brief stress. It is designed to focus on more sustained changes in heart rate, which are more likely to indicate a health concern.