Login Approvals force you to enter a random security code sent from Facebook to your mobile phone in order to log into your account. Enable Login Approvals by selecting Security from the Facebook Account Settings menu and clicking Login Approvals. When you check off the dialog box, you’ll be asked to enter the country code and phone number to which Facebook should send your secret code. Facebook will then send you your secret code and ask you to enter it on the next page. After entering your code, click Next and then Save Changes.