Facebook can tell you when your account is accessed!

Login Notifications:

Nice simple one.
Under the Security tab, in Account Settngs, you’ll find the Login Notifications.

Enable this and Facebook sends you a little message when a new device accesses your account.
The notification can be sent to you by email but that could get caught in spam filters or be delayed some hours so I’d send it by SMS as well.
This option allows you to be a little bit more aware of what is happening on your account. If a hacker gets hold of your account you can be notified immediately (I get the message within seconds) and take action to change your password, for example.
It is important to note that this only notifies you of new devices connecting to your account. If someone aims access to your PC and accesses your account from there, you will not receive a notification.