If you just wanted to return a Status - a Device based on this Template has an Alert, you still will have to do a 'get alerts' on all Entities first, but your service can then examine the returned information and create a true/false response or something like that, or a count etc.
So you get one single result back.
Sorry when I say alerts, I mean alert definitions. The alerts defined on the template. I don't want a history of alerts. I just want to see that this property has an alert defined and what is the criteria for that alert, etc... Does that make sense?
I need a mashup that allows the user to create, disable/enable and delete alerts. I want them to be able to view all alerts defined for all device types. And add alerts by template or thing.