https://www.theverge.com/circuitbreaker/2017/11/13/16644484/google-assistant-broadcast-google-home-intercom

Last month, Google announced that users with Google Assistant would be able to broadcast messages via Google Home devices, and now that time is here. Google has begun rolling out an update that will allow you to use your Home devices as an intercom system within your apartment or house (or office, if you hate your co-workers).

You can use Assistant on your smartphone to send messages to all Assistant-enabled speakers within your home, and with certain commands, like announcing it’s time for dinner, the Assistant will ring a dinner bell on every speaker. You don’t even have to be home to broadcast; the feature will work from anywhere with a cell connection, which is a nice touch.