Google announced several new things at Google I/O 2014, and one of these is that its HDMI plug-in device Chromecast will be able to provide casting functionality even when an Android device and the Chromecast are not connected to the same WiFi network. Previously, this was confirmed to be done through geo-location data, whereby Chromecast will authenticate with the device by confirming they are within the same vicinity. It turns out that Chromecast will also be using another technology altogether: ultrasonic tones.
Through this authentication method, Chromecast will emit ultrasonic tones from the TV’s speakers, which will then be “heard” by the Android device’s microphone, which will then lets it pair with the TV. Upon successful pairing, the android smartphone or tablet can now cast video content to the TV set, even without actually connecting to the current WiFi network through the usual means of authentication.
Being outside human audible range, users will not be able to hear the authentication sounds, although it can easily be generated and picked up by the respective devices’ mics and speakers. Observers point out that Google acquired SlickLogin earlier this year. The startup ran a technology for authenticating to websites using one’s smartphone or mobile device, and this was done through ultrasonic waves.
Notably, the use of ultrasonic tones is not necessarily new for Android or other platforms. Some app makers have relied on ultrasonic for cross-device functionality and compatibility. One good example is the 2012 Furby, which used an “ultrasonic frequency emission system” to communicate with Android and iOS devices, as well as with each other. This ensured maximum compatibility regardless of device capability (since not all devices may have Bluetooth, for example).
The only limitation I see at this point is during instances of excessive noise or improperly positioned microphones (such that if it’s blocked by a user’s palm or fingers), since even ultrasonic tones can be drowned out by too much noise.