the only places I can think of where it is illegal for you to just get up and leave (without like paying for something) is jail or during a filibuster.
It was in my University. Professors had 10 minutes to show up before students were allowed to leave. If they had a doctorate, we had to wait 15 minutes.
One time we had a block class and we waited outside for 20 minutes and no one showed up but the door was open so we all just went in and worked on our projects but while also using our phones. Then when the second half started the vice principal came in and was like " your sub left already? "
Moral of the story, its less suspicious to use your phones in the classroom than to noisily walk around the halls.
Because sleep
Moral of the story, its less suspicious to use your phones in the classroom than to noisily walk around the halls.