The evidence that (a) we simply cannot multitask, and (b) in-class electronic devices probably hurt students as learners more than they help them, continues to mount. This is an issue we've addressed before. What options are there besides an outright ban on devices? One position: "it's you're funeral". Some require students to post their electronic notes. Others try to turn the technology to their advantage, allowing students to send questions electronically.
I don't think I can enforce a 'no devices' policy. But I do think I can underscore the costs, both to students using the devices and to others, of their use. So I put the following statement on my syllabus and mentioned it to students:
I am sometimes asked if I have a policy regarding the use of cell phones and other electronic devices in the classroom. My policy is that (a) I cannot prevent you from engaging in behaviors that contribute to your academic failure, but I would encourage you to read this: http://bit.ly/1ihJUxL, and (b) your use of such devices must be consistent with the policies regarding respect, particularly provision 5.
Provision 5 reads: " You will respect my time and the time of your fellow students by helping to make our time together as productive and conducive to learning as possible." Note that the link takes students to brief summaries of research indicating that we not only are poor at multitasking, we greatly overestimate our ability to multitask productively.
I noticed far fewer students using their phones and electronic devices in my class this quarter. I'm not sure which had the greater impact: provision (a), which concerns the impact of device on students' own learning, or (b) which concerns its impact on others. But maybe just by providing this information, enlightened self-interest and peer pressure did the trick?