I upgraded one of our client's servers a couple of days ago by pushing all of its data onto a new image on AWS.  Since I re-enabled Observium monitoring on it (same IP address as the old one), I've been getting a "device rebooted" message every 5 minutes from Observium.

Observium :: Network Observation and Monitoring

Device Rebooted : hostname 1 day, 18h 17m 23s ago.