I was trying to setup an alert that would show up/down and then when it came back up if it had rebooted show that somehow.
I didn't find a good way to do this so I setup up/down with a LastBooted variable being displayed. This way if the last boot showed as the current time/date I would know it had just rebooted. However it seems that it doesn't poll the device before it sends the message. So my up message with LastBoot shows the wrong info.
Could you possibly set an SNMP trap to send when it reboots?