It's a program you sign up for on their website, choosing what airports you're interested in. You download it to your computer and when there are ding fares available, the icon pops up on your tool bar and you hear the ding sound. When you click on the icon you are taken to the webpage that lists the current ding deals from your airport. They are limited time only deals so you have to be quick, but we've gotten some great deals this way. Flew from Birmingham to Orlando once for $49 one way, and once to Tampa for $25 one way. The Transportation board probably has more info if you're interested.