This app has a time-based code generator called Code Generator. Even if you are not online, it creates distinct login codes every 30 seconds. Consequently, you always have a code available.
How does the code generator work?
You must enter your Facebook account information, including your username, password, and email address. A secret key that you will use to generate codes must also be entered. Your account will store the private key; no other device can access it.
You can generate your codes once you've filled out all the necessary information.