When hub loses the connection with the server, Ajax apps can notify the users using a standard push-notification sound or a siren sound (enabled by default).
To disable the siren sound when hub loses the connection with the server in the Ajax app:
Go to Service settings of the hub (Device
→ Hub → Settings
→ Service).
Select menu item Server Connection.
Enable the option Receive events of server connection loss without alarm.
How to know if a hub has lost its internet connection