If you access your Facebook account from a computer or a device that you have never used to access Facebook before, then Facebook can notify you. This is a important measure in mitigating hacking attacks on your Facebook account. Here is how to enable this feature :
- Login to your Facebook account.
- From the top-right of the Facebook web page, choose Account → Account Settings as shown,
- Under the Settings tab, you would find Account Security. Click on the Change link in front of it Account Security,
- Choose Yes from the options and click Submit button as shown,