Most of the questions you were asking about functionality are covered in the following community FAQs. (The topic title is a clickable link)
Before you start though, I will say that the ADT model hub has to be a replacement for your existing hub. You don’t use them both together. The ADT dual logo sensors use a completely different proprietary frequency, neither zwave nor Zigbee, so you have to have that model hub in order to be able to communicate with those devices. And those are the only devices that can trigger notification to the monitoring center.
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And the following community thread is the long discussion thread by people who have actually purchased the system. So they can answer more questions there.
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As far as “easily move” devices from one hub to another, nothing has changed in that regard. Smartthings does not provide a migration tool. They’ve often said they want to, but they’ve never done it. So you have to individually exclude each device from the old hub and then individually add it to the new hub. And rebuild all of your automations. It’s very annoying, but there are certainly people have done it, and again you can ask in the discussion thread to see what kind of experience people had.
So you have to individually exclude each device from the old hub and then individually add it to the new hub. And rebuild all of your automations. It’s very annoying, but there are certainly people have done it, and again you can ask in the discussion thread to see what kind of experience people had.