The short answer is, you don’t.
The main selling point of this new version of the hub with ADT is the central monitoring that is available, with cellular backup and an option for fire monitoring too (which wasn’t available with any previous versions of the ST hub).
Presumably to get ADT on board they had to separate the ST and ADT functions of it because, frankly, ST has seemingly never-ending issues related to reliability.
The longer answer is, you can check this thread and talk to the people that have the adt hub to see whether they’re getting it integrated into WebCoRE in such a way that you could get z-wave sirens to go off when the ADT hub’s security alert is triggered.