As a security measure, Facebook provides you with a service wherein you can set notification when someone else access your Facebook account.
Facebook detects when an account is accessed from a geographically different location, or from a device new for the account.
You can set to receive either a text message on mobile or an email notification.
Here is how you can enable this Facebook feature,
1. Login to Facebook and go to Account Settings>Security.
2. Click ‘Login Notification’. Set the desired mode of notification you want to receive when a potential attacker accessed your Facebook account.
You can select either or both Email and Text Notification.
3. Hit ‘Save’ and you’re done!
By receiving notification, you get the time to gain access or change password before an attacker does any harm to your Facebook account.