Amazon is speeding ahead with the Echo line. From the original Echo, to the Echo Dot, the upcoming Echo Look and the Echo Show, to the Dash Wand - the Seattle giant is making an Alexa-powered device for every situation and, unlike some of their other devices (ahem, Fire Phone), they're dominating the market.
Not only is Amazon creating new products seemingly every few weeks, but they're also constantly adding new features to the Alexa platform as a whole. Today the company is announcing the ability to use multiple Echo devices as an intercom system within your home. Simply ask a device to call one of the other devices in your home and it will start ringing, allowing the person in that room to answer and carry on a conversation with you. To make the most use of the feature, you might want to rename your devices to represent where in the house they are located, but otherwise the process is straight forward and handy.
Amazon also added the ability to "drop in" on other devices in the home so that the other party doesn't have to actually answer. There's some privacy concerns with this since it's possible the remote user won't know they're being listened to unless they look at the color ring, but this feature requires you to actually activate it within the Amazon app.
It's important to note that this feature is currently only supported on the original Amazon Echo, the Echo Dot, and the Echo Show. It's currently rolling out to the Amazon Alexa app and to the devices, so if you don't have it right now you should have it soon.