Just not bringing the devices should be enough.

I regularly advocate for offline moments so I definitely agree on the "how" ... but that's still not my point though.

What I was trying to highlight was that HOW depends on whom you are talking to. Here they just mentioned a deep behavior problem. Saying "just" or "simply" or "should" or "ought to" or anything implying it's really not that hard is probably not going to be encouraging to them.