Colleague Instructors, How do you maintain the interest of the student who has knowledge of a subset and 'checks out' until a point in the course that will present new information to him/her?

I welcome feedback from colleague Instructor on their approach to students who monitor / use their personal devices (smartphones, tablets, laptops) during class. Do you allow use? If so, at which point do you deem use excessive? At that point, what keywords or feedback is given to the offending student? Thanks.