Google revealed yesterday that it will allow its Chromecast streaming stick to cast content without being on the same Wi-Fi network as the device sending it. According to a session Thursday, the Chromecast will be able to pair without Wi-Fi, or even Bluetooth, via an unusual method: ultrasonic tones.

GigaOm reports on Thursday's Google I/O session with Chromecast engineering manager John Affaki, in which he described the use case for multiple devices queuing up content to one Chromecast. At a party, for instance, not everyone who wants to throw a YouTube video up on the TV with their smartphone is going to have the home's Wi-Fi password. The product team needed a new way to make the devices and the Chromecast talk.

In the new system, Chromecast owners first allow support for nearby devices. A nearby device then requests access to the Chromecast, and the Chromecast plays an ultrasonic sound through the connected TV's speakers. The sound is then picked up by the microphone in the device, which allows it to pair with the TV.

Based on a demo from a Google engineer last year, the sounds aren't just used for simple confirmation that two devices are in the same room. Instead, the Chromecast likely uses a combination of tones that can be encoded with data to communicate a message. This limits the bandwidth and reliability of the transaction, but for a simple exchange like pairing, it's a fine solution. Below is a video of Boris Smus, "sonic networking" creator, using tones to send messages between a computer and a phone.