Smart group based on check-in status

Hi all, I was wondering if anyone has a way to group devices based on how long they have been checking in outside of my network. Here is an example: I have a computer that has been checking in from the outside for 2 weeks straight without ever coming into my network. How can I track this? I was thinking of a script that would track ip's for a period of time ( or check-in quantities) then kick off a policy that would flag the device in some way that I could set it to a smart group. Anyone have any thoughts?