Although I lecture in a college environment, out students are subject to military discipline, and one of the rules is no mobile phones in the classroom / lecture hall. That includes our international students, currently Saudis, and is a rule they struggle to obey.
I was showing a video today and, as usual, the curtains were drawn and the lights switched off.
Within seconds of the video starting, from my vantage point at the lectern, I saw several of the students with their faces bathed in the light from their mobile phones, which they hide in their berets, blissfully unaware that they were as identifiable as lighthouses.
I paused the video, brought the lights up and demanded to know if anybody was using a mobile phone, to be faced, unsurprisingly, with a sea of innocent faces
Imagine their surprise and consternation when I called all five of them out, by name, and told them to bring their phones with them.
Bless their cotton socks, they hadn't a clue as to how I knew