dude, get their IP

Make a class in php for checkin IP!

Compare if the IP is from the same country! If its not, then you know what to do!

Genrally, you will only need to match the first part of the ip address which will give you the location(country of your user)!

Moreover, you can use cURL to generate an automatic lookup on a specific site such as (whatsmyip.com) and use regular Expressions to get the location! Or simply if you have a database of IP formats and their location, this could help also!

Now, that will make your php page loads damn slower! what you can do is,
When the user logged in, he get a message like
"Checking Account Settings" and some animated progress bar during which you check the logs of which IPs used the account and throw them to your php Class.