Google wants to make the experience of using Chromecast more social. To do that, it's opening up the $35 device to everyone in your living room, regardless of whether or not it's connected to your Wi-Fi network. Announcing the new feature during yesterday's I/O keynote, Chromecast product manager Rishi Chandra said, "We’re using a variety of different technologies, which allows us to authenticate users in the same room as Chromecast." But considering how cool one of those technologies is, it's surprising that Chandra didn't offer more details.

GigaOm says Google's using ultrasonic audio cues to help make the connection between smartphones, tablets, and your TV. These sounds — emitted by the TV that your Chromecast is plugged into — are completely inaudible to the human ear. But the microphone in your Android phone can hear them just fine. Once you've enabled support for "nearby devices" in Chromecast settings, anyone in the room can send what they're seeing (or listening to) to the big screen for everyone to enjoy. Googler Boris Smus wrote about ultrasonic networking last August, and it seems the Chromecast team has now fully embraced the concept. As a fallback, Chandra noted that users will also have the option of entering a PIN to establish a link with Chromecast. And there's always the option of just asking for a friend's Wi-Fi password, or giving out your own.

Chandra said the feature will be arriving later this year. First on the agenda are popular requests like mirroring and a new "Backdrop" mode that lets you customize Chromecast's background with personal photos and other content when you're not actively streaming something.