Go to Assets and right click on the target agent machine and click properties
On the general tab click Configure Health
Configure the health timeouts to suit your own enviroment and requirements and select on what agent state an alert should be generated
Now we need to create a new alert if you click on alerts and click new alert give it a name and description, Now click on the filter tab, we're going to filter for event type communication for instance. Set the appropiate settings for Email and/or SNMP and you're done.