When listening to an ebook it is easy to fall asleep, either on purpose or by accident.

I suggest monitoring awake/asleep state and pausing the ebook reader.

Monitoring could be done through one of those smart watches that all seem to create graphs of how long you have run and for how long you have slept. It could also be done through listening to breaths or watching eye movemements.

The ebook reader could be paused or a book mark could be set.