I have been wondering if some of my students who demonstrated zero knowledge in class but ace in-class exams were doing something like this. I figured something like a hacked out google glasses would do the trick.

They probably just have huge pools of all your previous tests that they share and memorize.

Make them wear school-provided inside-ear headphones to hear the exam.

I did not use them, but saw them using wireless, pill shaped speakers they inserted into their ears they had to get out with a magnet.