On the Device Manager page, open a specific device to edit (a device action button > Edit). Then, on the device edit screen, go to the Alerts tab. In the Send Alerts to Group(s) section, click the Add Group button and select the check boxes related to the necessary group. You can select multiple notification groups to receive alerts.
You also can configure the Escalation option that allows you to start alerting if downtime remains for longer then a specific period of time. For example, Group A could be notified immediately, Group B after 10-minutes of downtime, and Group C after 60-minutes of downtime. Alert escalation time intervals range from immediate to three hours and are available in 10-minute increments.