Do your students pay attention when you speak?

As I am not a teacher, I can't tell you any experiences, so I'll just give my thoughs on how I would deal with such a situation. I know this is not exactly what you asked for, but I hope it can be at least partially helpful.

I think the situation consists of two perspectives: First of all, how you feel; secondly, how you think the students should feel and behave.

To the first point I have to admit I don't have a lot of experience: I imagine it can frustrating to teach when nobody seems to listen. This will probably be dependent on the self-confidence of the teacher and can be a greater or a smaller problem. This is something you can say to your students in a message like "I'm feeling frustrated if you don't listen to me, could you please do so?". Formulating a message like this often helps the addressed persons to understand your feelings and is more likely to work than an unpersonal message, it would additionally not have to be a "firm" message if you don't like to give one (you'd just talk like you'd normally talk about your feelings).

To the second point I would say you don't have a lot to do. You try to let them profit from your knowledge and the effort you have made to work into your curriculum, so your lessons are an opportunity for them. If they decide not to follow them, it's only their problem. You could point out once or twice that this could have consequences for them you can't regulate (such as not passing final exams or not having the knowledge they apparently wanted to gain). After that, you don't have to say anything more to this.

From a student perspective I could say to you that students find many ways to get distracted in front of the computer, even if they value you and your lessons. This happened to me at least once as a student in a class where I really liked the teacher but somehow thought it would be "cool" to do something else - the teacher then noticed it and asked my to either focus on him or turn of the monitors. I followed his request because I thought over it again and noticed I was really interested in the topic.