So wait what if you move to a new house and buy a new computer and use your key?
This is a post I'd expect from someone new.
You've been here... how long?
You may only use an ID on one network at a time. If that network stops using it, another one is allowed. If both try it at the same time, it will cause the first one to get an authentication error and kick them out. This will also catch Badspot's attention.
Even if it moves to another network while the first one is no longer using it, Badspot can compare the distance of the two IPs.
You cannot go across an entire country in 5 minutes.