Alexa is now able to Drop In on all of your Echo devices at once. The Drop In feature, which lets you begin communicating through your Echo without needing anyone on the other end to pick up the call, used to only be a 2-way conversation between 2 devices. With the addition of Group Drop In, as Amazon is calling it, now all Echos can communicate simultaneously, like a multi-point intercom system.
To use the new feature, simply say “Alexa, Drop In on all devices.” The first time you use it, you’ll be asked to enable enhanced communication features that require Amazon’s cloud servers. The servers are essentially acting like a phone operator that is taking all the individual microphone feeds from each Echo device and merging them into a single audio feed that is sent back down and played out of all devices.
The important thing to note here is that, for the cloud server to do the merging necessary for Group Drop In, it has to decrypt the audio in the cloud and then re-encrypt the new audio feed being sent back down. While Amazon says they aren’t storing any of your calls, they are being upfront with the privacy implication and telling you that there is a literal machine-in-the-middle that all of the audio is passing through. This is different from regular Drop In calls which are, and will remain, end-to-end encrypted with no machine in the middle decrypting anything.
At any point, you can go into the Alexa app and disabled the enhanced communication option which prevents Amazon from decrypting your communication audio and disables Group Drop In. The feature is found in the Alexa app under Settings > Communication > Enhanced Feature. What you can also do from the Alexa app is disable Drop In on specific Echo devices so that they are not included when you ask to Drop In on all devices.
It would be nice if it were possible to selectively Drop In on a subset of Echo devices, perhaps by creating a custom grouping of devices that can be called out by name, such as “Alexa, drop in on upstairs devices,” but that doesn’t seem possible. It’s all devices or one device right now. What are also not supported at this time are Group Drop In capabilities through the Alexa app or Fire TV Cubes. Neither the Alexa app nor Fire TV Cubes can initiate a Group Drop In or receive a Group Drop In. This only works on 1st-party Echo devices right now.