When you set up a TPD based on the priority of the ticket you can do something called an Escalation Alert. This is a feature that gives you the ability to send a notification to the Agents inbox at the time the TPD expires for a particular ticket.
To enable this feature when you set up your TPD for a particular priority type all you have to do is turn on the Escalation Alert for that definition.
When TPD’s have been set in place you can choose if an escalation alert needs to be sent to an agents inbox when the ticket response or resolve threshold has been met. What this means is when a ticket has passed the due date based on what it was configured at then an alert will be sent to the Agents inbox alerting them of the past due date and that the ticket should be responded too or resolved immediately.