I’d like to add one more thing that is noteworthy, and I’m also hoping that bringing this up frequently will help get it documented (@jim? @unixbeast?) as an official Capability.
i.e., Unlike Smart Home Monitor, the ADT “Device” appears to be implemented to claim a (undocumented) Capability “Security System”. That means that SmartApps can control it, but do so in an entirely different way than the (undocumented) methods used to control SHM. I wonder SHM will ever be modified to be in compliance with this new Capability!