@IanWedlock If you are using an ADT Smartwatch 3000 (more commonly known as a Honeywell/Ademco Vista 20p) you can definitely use the entire security system in conjunction with SmartThings. Please see the thread here: ADT Smartwatch Pro 3000EN Integration
Main post with instructions is here: DSC/Vista Alarm Smartapp and devices based on AlarmServer
It requires running software called AlarmServer, so you will need a spare computer and an Envisalink 3 module to get the alarm panel on your network. Good luck!