Google home broadcast is a neat feature rolled out a year ago (Fall 2017) without a lot of fanfare for users of Google Assistant, and Google Home devices, and it does NOT seem to have improved since.
It's simple - just say "Ok Google, broadcast." and the next few seconds of what you want to say can be echo'd through-out the home. Let us know if you hear this has improved?
Broadcast is simple store and forward - it records your message and plays it out of all your home devices. There's no direct duplex (two way) communication - it's the Google's version of a megaphone. But it could be more.
Amazon is the winner here in our books. Just like Google home, with Alexa you can say "Alexa, tell everyone..." or "Alexa, broadcast..." - just like Google this method broadcasts to every device in the home. But Alexa can do more - with multiple echo devices you can say "Alexa, drop in on XXX" where that XXX is a room to go live speakerphone.
One of the amazingly cool features (or creepy depending on your perspective) is the way you can use your mobile phone to broadcast to your house. On the way out the door at the office you can tell everyone you are heading home - if there are any last minute needs for dinner, now is the time to catch you en-route!
But I like the room to room live intercom though for the hands free convenience - if people have thier hands full, they have to decide to give you a call. But at least they can do that hands free right?
SlashGear has some notes on sound effects which will be added to certain trigger phrases (like calling the kids for dinner) - click here for more information.
Google should add a "drop in" full duplex intercom feature. We've been waiting a year - come on Google catch up! Sure there should be a Do-Not-Disturb option (for times you do not want to be inter-commed) but we're looking forward to an improvement.