Triggers are things that "fire". They are the ones that look at item data and raise a flag when the data does not fit whatever condition is defined. As we discussed before, simply gathering data is nice, but awfully inadequate. If you want anything past historical data gathering, including notifications - there would have to be a person looking at all the data all the time, so we have to define thresholds at which we want the condition to be considered worth looking into. Triggers provide a way to define what those conditions are.
Earlier, we created a single trigger that was checking the system load on "A Test Host". It checks whether the returned value is larger than a defined threshold. Now, let's check for some other possible problems with a server for example, when a service is down. The SMTP service going down can be significant, so we will try to look for such an event now. Navigate to Configuration | Hosts, choose Triggers in the first dropdown and click on the Create Trigger...