You would need to use a community created app called ADT Tools. Basically it sits on the Smartthings side. When an alarm event is occured it will react and do certain actions for you. They range from turning on lights/flashing lights, activating additional smartthings siren, notifications and more. One thing to remember is it is cloud based so though the alarm side will always work well and function locally. ADT Tools and the actions it will trigger will be subject to Smartthings Cloud reliability. It isn’t normally a problem, but it can happen.
Details about it are here in the release thread
You an also check out Things That are Smart for additional info about custom apps and how to use them.