Removal of old system

I've been test driving SS for a couple months but haven't activated yet since I still have some sensors to install (after figuring out where to install them!) and I need to cancel ADT. I'm now ready to put ADT (and their $70/month fee!) in my rearview mirror but am concerned about removal of their equipment. We've had the system for probably 12+ years and some of it is hardwired. After I cancel (hoping to this weekend), what's the best way to remove the system? I would ask ADT but I don't think they will be helpful after cancellation. My fear is that I start taking down sensors and it triggers the siren. System has a battery backup as well.

Thanks!