This is a great event to add to most of your alerts.  It's helpful to be able to see if there's an alert condition under way, and a quick glance at the tray can let you know by using the event.

 
The Tray Icon Change notification will do one or both of the following:

Change default icon to red during alert conditions

If you already have MultiPing showing in the tray, this will change the existing green icon and add red to indicate that an alert has fired.  If you don't have MultiPing in the tray already, then a red icon will be added to the tray.  When the alert condition(s) are over, the icon will change back to green.

Popup message in tray

This shows a "balloon" message coming out of the tray.  Not all versions of Windows support this message (ie: some versions of Windows 95), in which case no balloon will show.  Only one balloon can be shown at a time, so the newest balloon always wins (a new balloon message will replace an older one).

Variable substitution will be done on your message text. 

One of our favorite messages is:  Alert fired on $host, $date $time. This is a great message because it stays up until you acknowledge it, so when you come back to a PC, you can see what alert fired, what host it happened on, and what time it *last* happened.  This may be over a weekend, but the message will still be there telling you that an alert happened.