I suspect, but can't prove, that some of my students used their phones to access ChatGPT during an exam. Likely, they were using their phones on their laps when I wasn't looking, but I didn't get any direct visuals.
I think a fair way to respond would be to have the suspected cheaters come in for an oral assessment. See if they can answer the same question on the board in front of me.
What do you think is fair?