How does this work if the student declines to carry a mobile device? I own a smartphone so that I can receive SMS authentication codes from people like my bank,

How does this work if the student declines to carry a mobile device? I own a smartphone so that I can receive SMS authentication codes from people like my bank, who haven't yet grokked that SMS is insecure. But: that phone never leaves my home - I don't carry it around. It isn't a "mobile" phone. So that's going to be "Excuse me Miss, I can't run the app, because I don't bring a smartphone into class. Now can I please have a pee?"