If I can't hear the sound on the phone when viewing the live screen of Xiaomi Smart Doorbell 3, please refer to the following steps:
1. Check whether the Mi Home app turns off the doorbell ringtone (0%) or selects a lower volume;
2. Check whether the volume of the phone is adjusted to mute or the volume is lower;
3. Check whether the mic hole of the doorbell is blocked;
4. Close the app completely and then reopen it to see if the audio works;
5. Update the app and firmware of the doorbell to the latest version;
6. Check and adjust the permissions to access phone's microphone and speaker in your phone's settings;
7. Ensure that the Xiaomi Smart Doorbell 3 has the latest firmware installed. To check available firmware, tap on [ ⋮] three dots located at top right corner of the screen >> [Doorbell settings] >> [Device Info] >> [Firmware version];
8. We hope the above information is helpful. If the issue still occurs, please open the Mi Home app, and go to [Profile] >> [Feedback] >> [Other]. After submitting the user feedback, please have some patience and wait for future updates.