If a robot becomes inactive for any of several reasons the hub it reports to will generate an alarm.
"Hub update interval" determines the time when hub will generate the robot inactive alarm. When a robot comes up, it sends an internal message to the hub with its status and the next time the hub should get the same status message from the robot based on "Hub update interval" setting - which is (by default) 15 minutes. The hub expects to hear again from robot approximately around the "Hub update interval" x 1.5 (e.g: 15 x 1.5 = 22.5 minutes) and if it doesn't, then the hub does a robot check-in to check robot status. If robot is non-responsive to the hubs robot check-in, then the hub will generate "Robot <robot name> is inactive" alarm.
In either case, an alarm will be generated and visible in the alarm console (NMS Manager, SDP, UMP) and a nas auto operator can be configured to send an email notification to specified recipients.