AWS Service Health Eventsource - Report at AWS Device Group Level

You can choose how the AWS Service Health EventSource is applied - by default, it doesn't apply to anything.  By editing the EventSource AppliesTo field, you can have it only apply to the AWS Device Group itself, so that you only get one alert per event.  

The "Applies To" for the Datasource is set to my AWS Device Group, but it created alerts for each device in that AWS Account, in that region...  I will add the "hasCategory("AWS/EC2")" so it won't alert on EBS volumes, but it's still going to alert once per device, right?

I see, yes - if you apply to a group, the EventSource will apply to each device in that group, which is why you're getting duplicate alerts.  You'll need to make sure the EventSource only applies to one device to avoid the duplicates - a few ideas on which device to apply to are: a billing device if you have one in monitoring (as that is unlikely to come & go), you can add 'status.aws.amazon.com' as a device and apply it to that, or you can just pick any non-temporary device in your AWS Device Group.  Does that make sense?

We don't have any devices that would permanently be in an AWS account (would it have to be per region too?).  Possibly the collector boxes, but I'd have to make the connection between the AWS EC2 device & its matching device that is the collector box...