If we get to the point where even that doesn’t work then we’ll be at the point where a camera in the room with an AI analyzing eye movements should be able to detect it. And no matter how advanced they get they’ll still need to radiate heat, so a thermal camera should work. If that fails, industrial CT scanners are getting cheaper and cheaper.
Heck if it gets too bad there’s always mm wave body scanners and a set of cheap glasses kept at school.
We had a 'fix' for this back when they checked your TI83. It's a 2 line basic program to display "MEMORY CLEAR" the exact same way as if somebody had spent the time to find the actual memory clear function in the settings.
Also I was in high school in the prime time for this hack and I never saw someone actually use it despite the stories.