After enrolling a mobile device to use for authentication, you have two ways to authenticate: Duo Mobile Push or Duo Mobile Passcode. If your mobile device is a smartphone, you can also authenticate by getting a phone call from Duo. Choose the method that sounds right for you:
Duo Mobile Push lets you authenticate with the push of a button. It's the easiest form of authentication. It requires either cellular service or a WiFi connection.
Duo Mobile Passcodes are one-time codes generated on your mobile device and can be accessed even without an internet connection or cellular service.
Call Me is an option that works for smartphones and landlines. Duo will call the phone number you enroll, and then you will tap any key on that phone to authenticate.