A few weeks ago I realized on my phone I can, from anywhere, say "Ok google, broadcast" and then say a message. That message gets played back on the Google Home devices.

My kids weren't replying to text messages about being ready to go to an appointment that we were pressed for time on, and I was on the way home, so I did that to tell them to get ready. A few seconds later I get a text from my wife: "How'd you do that?!?"