There are two extra feature for to get the alert for the incomplete tickets to the Head of the department.
- Age report
- No user alert.
To enable the option Go to -> Reports -> Subscriptions.

Age Report:
If you enable the age report, the Manager role gets the reports by email for the tickets which are in On Hold or Open status for more than 6 hours.

No User alert –
No user alert is used to make an alert to the Head of the department if the user is not available to get assign ticket in a particular department.
