LM - alerts

When I go through the documents regarding Alerts, I understood that the threshold for a particular Metric/Datapoint can be set in the Datasource itself. I have made an example alert and got an clear idea about the concept.

I have a doubt whether can we create an alert for a widget. For example, I have a Gauge widget and represented CPU percentage over there. So how can I set my alert only to that particular widget if my CPU percentage crosses 60% or 90%.