However, Amazon announced this week that all Alexa-capable devices will now support the feature, which in effect works like a one-way intercom system. For instance, if you're downstairs in the kitchen and you have Alexa devices spread throughout all the bedrooms and shared spaces within the house, you could say "Alexa, tell everyone that dinner is ready", and your message will be broadcast through all of the devices within your home at once.
You can send these voice messages either directly from an Alexa device, or from within the Alexa app for iOS or Android. Amazon also gives that example of selecting a movie with your Fire TV Cube and telling the laggards in your family that "the movie is starting" to get them to place their rumps on the couch for some Avengers: Infinity War action.
All in all, it a nifty feature that is useful for anyone with an Alexa-powered device, be it one made by Amazon or by a third-party like Sonos or Bose (among many others, like the Facebook Portal). According to Amazon, Alexa Announcements are available to use on "certified Alexa built-in products to implement and new ones that pass the provided self-tests and certification."
For OEMs that want to learn how to implement Alexa Announcements on their devices, Amazon is providing the tools to do so right here.