Does the Bluetooth of the phone need to be turned on all the time when using the wearable device?

Disconnection between the device and the phone will mainly affect the following functions:
1. Unable to update the firmware on the Mi Fitness app;
2. Unable to update weather information;
3. The sports and health data cannot be synchronized to the phone immediately, and the information will be lost forever after the device is restored to factory settings;
4. Unable to receive notifications from the phone and unable to use the Find phone function.
Functions can be used without connection:
1. Some basic functions can be used without the connection to the phone, such as Stopwatch, Timer, Alarm, NFC, etc;
2. Some monitoring functions (heart rate monitoring, blood oxygen monitoring, etc) and data recording functions (sports data, sleep data, etc) just can be stored for a short time. You need to connect the device to the phone to synchronize the data regularly.
Note:
It is recommended to keep the Mi Fitness app running in the background of the phone, avoiding some software cleaning processes or interception. Please turn on the Background permissions for the Mi Fitness app.