You will be able to know If anybody come to know your password of facebook account and log in or enter in to your account without your permission .To get this service ,first of all you will have to log in to your account.Then you will see account on right side and find account settings and click on it.Now click on change of account security. Then select yes and click on submit. Now log out from your account and log in again.there you wil see a page as register this computer. In this page write a name on computer name box click on save.
From now,whenever you log in to your account a e-mil will be sent to your