Are you wanting to get alerted when a device isn't sending messages? Or do you want to get alerted when a Rule isn't triggered by those messages?
If it's the rule you are concerned about, do you want to check for every message, or just check periodically and how often do you want to be alerted? Do you want to be alerted at every failure? Or maybe hourly with something like:
Rule 17 Processed 652 out of 798 messages
Do you want the missed messages included in the alert?
Is this for rule trouble-shooting purposes? There might be easier ways to do this.