Most people using Duo two-factor authentication use either the "push" feature (where Duo sends a confirmation prompt via an app on your phone) or "call" feature (where Duo calls your phone and you confirm login via the dial pad).
In cases where your connectivity may be poor, such as traveling in areas with poor reception, additional options may help. All of these options use the "Enter a Passcode" section within the Duo authentication screen, shown here:
Option 1) The Duo app can be used to generate a one-time passcode that you enter into the "Enter a Passcode" section of the Duo login prompt. To do this, find the "Duo Mobile" app among your phone's apps:
Within the app, click the key icon shown here to generate a passcode.
Option 2) The Georgia Tech Passport website can be used to generate a list of emergency codes that can be used in the same way. From Passport, choose
Two-Factor Authentication -> Generate Backup Codes
You'll be shown a list of 10 codes -- it's best to print these out in advance -- as you use them, mark them off (each code can be used just once).
Option 3) "Hardware tokens" such as Yubikey [ https://www.yubico.com/ ] can also be used -- these essentially automatically generate and enter codes like those mentioned above. These are very convenient but cost extra, usually in the $20-40 range per token -- this expense would need to be borne by the school/unit.