With that being said, I find these kinds notifications to provide more false positives than correctly detecting downtime. That ends up costing more time checking/double checking.
On the other hand, if you are running a service with no users and you have downtime... did you really have downtime?
If you run a service and you have downtime and no one reports it, did you have downtime?
I don't even check for my services. If something goes down, I'll find out via email from one or more of my customers. It happens very rarely.