The free Google Authenticator app generates two-step verification codes on your Android phone or tablet. As you probably know, Google's two-step authentication process requires you to enter your username and password, and then click or enter an authentication delivered to your mobile device via mail, text, voice, or Google Authenticator.
Learn the two-step: It's easy to use Google Authenticator, but for those users still wondering what "two-step verification" is, a video tutorial, setup wizard, and plenty of clear explanations dispel all mysteries.
Security: Google Authenticator generates new codes every 30 seconds and requires codes when you or anyone else tries to sign in from any other computer. A backup phone number covers your assets.
Code break: To make things easier, you can temporarily suspend code requirements once per session per computer.
PC required: You must visit accounts.google.com/security on a computer to set up Google Authenticator with your Google account.
Re-entry: You can manually add accounts via QR Code or provider key or tap your Google account to continue setting up your account on your computer, but the process is cumbersome and requires a lot of entering and re-entering of passwords, codes, and so on.
It's a little different signing in with Google Authenticator, as the app's documentation describes, but it's actually a bit easier and a lot safer than other methods, once you're used to it.