These days hackers and some other are so smart that may steal your account passwords and you never get to know about it, as they keep on logging to your account from other computers without your knowledge and peek into your account without your permission.
So, if any one else login to your account from some other computer other than the registered one or the some other mobile phone other than your registered mobile phone you will get notified via email.
After you have successfully log in. Perform the steps below
Click Account button at the top right corner (drop down menu appears)
Click Account Settings
After you have clicked Account Settings, the “My Account” page will load. After it has fully loaded, (under Settings tab) scroll down to the bottom of the page and look for Account Security, then click change (image below will appear)
Facebook will ask you “Would you like to receive notifications for logins from new devices?”. Select Yes and click Submit. In order for this setting to work you need to logout from facebook.
Login to Facebook again. After you have logged in a page similar to the image below will appear. It will ask you to name your device.
A. Enter the name of your device.
B. Check the Don’t ask me again from this computer
C. Click Continue
Thats all folks ; ) ..... enjoy safe facebooking