Downtime monitoring enables our customers to monitor for the lack of metrics coming from a resource. It may or may not mean that the resource is down, but you will be alerted in case there are no metrics coming in from that resource from a specified amount of time.
Also, please keep in mind that depending on which resources you are monitoring, data might have a 1, 5 or longer minute delay. Please set your alerts accordingly.
Downtime monitoring is easy to set up. Under Monitoring - Create Policy, choose Downtime Monitoring, select the customers/projects or resources you want to monitor and how you'd like to be notified, and save. That's it!