I agree, but I'll argue that this is not responsive to my question, nor a reasonable goal in general. You cannot be _sure_ that a student isn't cheating without

I agree, but I'll argue that this is not responsive to my question, nor a reasonable goal in general. You cannot be _sure_ that a student isn't cheating without taking draconian measures, but you can likely catch a lot of lazy cheaters by applying imperfect methods. The problem comes when the methods are treated as infallible and there is no appeal process.