Today, Amazon started notifying Echo and Ring users of a new service that it's rolling out this year called Sidewalk. Sidewalk is essentially a proprietary shared network that runs on top of your personal network. According to the company, it uses a "small portion of your Internet bandwidth", although it obviously won't help you out with your internet bill.
Amazon didn't get too specific on how Sidewalk will improve your life, but you can check out the product page here. The firm says that it "helps devices work better", and can simplify setup, extend the range of devices, and allow your devices to stay online if they leave your home Wi-Fi, as you'll just be using someone else's.
According to the listing, it uses about one-fortieth of the bandwidth that a high-definition video would use at 80Kbps, although it's capped at 500MB. That should be the same as about 10 minutes of HD video.
It's essentially creating a mesh network, and the more people that get on-board, the broader the reach will be. If you're uncomfortable with that, that's fine too. You can easily turn it off in the Ring or Alexa apps, although based on the listing, it does seem like this will be turned on by default. Amazon is referring to the Echo and Ring devices that support this as "Sidewalk Bridges", and it's pretty much anything from the second-generation Echo and newer.