Advice please - mobile phone in AS exam

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A friend's DC had AS exam today, and phone was in pocket. It beeped for low battery and, of course, that was noticed. She's been called in for meeting tomorrow. Has this happened to anyone? What are the consequences?

Ours put theirs in a box at the start of the exam- there are only usually about 10 who have forgotten to take them out of their pockets, not bad out of about 160.

Really though, by As level,having gone through mocks and GCSEs , they should know the ropes!