When an OnCallRecipient receives an alarm, it handed to the current OnCallList.

TheOnCallList sends the alarm to theOnCallContact with the highest priority. (Here, high priority means a low number for the OnCallContact with priority one will receive the alarm before an OnCallContact with priority two.) The users are contacted simultaneously if multiple contacts have the same priority number.

When the alarm is sent, a timer starts. The user or users notified for the alarm have a set amount of time acknowledge the alarm. If this time elapses and the alarm is not acknowledged, the subsequent user down the line, in priority order, is notified, and the timer starts again. This process continues until either the alarm is acknowledged, or there are no more users to notify.

To configure how much time users have to acknowledge alarms, change the Escalation Delay property in the OnCallRecipient. It defaults to 30 minutes, meaning an on-call user has 30 minutes to acknowledge an alarm before contacting the next on-call user.