Can I be notified of an SLA breach?
Yes. It is possible to build automations that send notifications of upcoming SLA breaches by using the condition Ticket: Hours until next SLA breach or to be notified of past SLA breaches by using the condition Ticket: Hours since last SLA breach. Automations run once every hour, which means an automation can send a notification as close as the hour before or the hour after an SLA breach.
For more information, see the article About automations and how they work.
Unfortunately, there is no native method to send a notification at the precise moment of an SLA breach or to use intervals smaller than hourly automations.
For more information see Creating and managing automations for time-based events.