This is a new feature. It's not working for me. You use your phone to broadcast to GHs. I've got the most up to date version of the GH app. Would someone please give it a try?
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Google calls the feature “Broadcast,” because it lets you broadcast a message from your phone and out through all of your Home speakers.
To use the feature, you just say, “Hey Google, broadcast ‘What’s everyone up to?’” and your message is supposed to automatically be sent through. It’ll be read aloud in the Assistant’s voice — not your own.
Google also took the stage to announce Broadcasts, a small addition that should come pretty handy in times – and pretty annoying at other times. With Broadcasts, you can send a message to your Google Home speakers and have it spoken out loud by the Google Assistant to everyone in the room. To send a broadcast, you just need to say “OK Google, broadcast” followed by the message you want the Google Home to speak out. It’ll be read aloud in the Google Assistant voice instead of your own voice, so it’s not simply broadcasting a simple voice message.
This feature, while it’s actually something really basic, can have many different utilities: you can use a broadcast for telling your friends something in another room, you can use one for waking up your children in the morning, and a lot more!