Back in April, Amazon announced a new feature called Announcements that let users broadcast voice messages to Echo devices. Although these could be initiated from a phone with the Alexa app, they required an Echo speaker for the message to be played out loud. However, the company is now extending the functionality to other devices with the voice assistant built-in.
Unfortunately, not all devices will be compatible with the new feature, as there are some prerequisites for them to work with it. Lastly, even if the device is technically capable of handling Announcements, the manufacturer would need to enable the functionality before owners can use it, so it may take some time before you receive it on your speaker.
- Alexa Developer Blog