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Chromecast’s Wi-Fi Free Pairing Works Using Ultrasonic Sounds

chromecast logoDuring last week’s I/O keynote Google announced that the Chromecast will soon allow users to ‘cast’ content from apps to a nearby TV, even if they’re not connected to the same Wi-Fi network as the device itself.

But just how will it achieve this? The answer might surprise you.

Until now, pushing content from an app, browser or extension to a Chromecast equipped TV has required both devices to be on the same wireless network. With that necessity negated, what’s to stop people passing by your house to rick roll you?

By using bat signals.

Chromecast to use ultrasonic pairing


In a session held after the main stage fun, the engineering manager of Chromecast at Google, John Affaki, gave further details on how the invisible authentication will work.

And in short it’s amazing.

The Chromecast will use ultrasonic sounds to form an inaudible handshake between nearby devices and your big screen TV, offering frictionless connectivity with supported apps and an enhanced social experience.

A unique frequency, imperceptible to the human ear, is emitted by the streaming device through your TV speakers. Ensconced within the sound waves is everything nearby mobile devices need to know in order to pair up. When your phone ‘hears’ an encoded trill, Chromecast buttons will appear active in supported apps and casting can begin.

The assumption is since people are in your home, and your Chromecast is turned on, you’re probably okay with them shunting content to the big screen TV.

Support for the feature will be rolled out to existing users of the media streaming dongle in a future software update.  The change should make it far easier for people to take part in a collective YouTube viewing fest, or fling holiday snaps for group viewing to the big screen.


Dog, cat and rodent owners worried about the impact the noise might have on their pets needn’t worry: an alternative Wi-Fi free method will allow an onscreen pin number to be used in place of the ultrasonic pairing.

Bat chatter aside, I/O saw a number of other features unveiled for Chromecast, including new customisation options, integration with Google Now, and Android device mirroring.

  • J Cav the Great

    That’s innovation.

  • Anthony Tumiwa

    i have ezcast, which can connect phone and TV without the need of wifi router, i hope the next generation chromecast can do that too

    • Jop


  • Cristian Otegui

    ES Explorer para Android permite enviar archivos desde un smartphone a otro smartphone a través del router del teléfono móvil. La única condición es que ambos equipos tengan instalada la aplicación y uno se conecte a la red generada por el otro. No entiendo por qué Google Chromecast necesita un router Wi Fi externo para recibir contenidos desde un smartphone.

  • Christopher Horton

    Ultrasonic networking is cool, but not new. The badBIOS rootkit worm uses ultrasonic networking to infect computers regardless of operating system by using internal motherboard speakers and microphones to spread, even in the absence of Wi-Fi or Bluetooth:

    • Ian Armour

      I read this article and that’s what I was thinking about the entire time. Doesn’t that seem a little odd…

  • Theodore Khachaturian

    It would be cool if google used this technology to develop multiroom audio for Chrome OS machines and the Chromecast to work together. It SEEMS like that would work, but i’m no software developer.

  • Patrick Fraley

    If they add a feature for Playlists, than this would be an awesome thing. Everyone at a party can add youtube videos or music to the playlist, without disturbing the currently playing tune :)

  • LeadTheLeader

    WTF? This is the most innovating feature I’ve seen in the whole year!
    Led Lampen

  • Mira Cabral

    Eu vi um toca discos “Do Espaço” que transmitia o sinal via wireless, era só sintonizar qualquer tocador FM no sinal do toca discos e então o som era reproduzido… Isso nos anos 60

  • Harvey

    Hopefully this should help us out in schools where the network keeps losing the Chromecast – something to do with our Smoothwall I believe.

  • Jeňa Kočí

    you mean inaudible for humans…

  • Cynthia Spann

    Im fixn 2 get a chromecast for my tv but dont have wi-fi I kno ill hv 2 get internet but would I have 2 buy a router or is there any easy way 4 me 2 do this im new 2 this

    • Darkschneidr

      Leaving out letters just makes you look ignorant, not cool. Stop being so lazy. Yes, you’ll need a router to update the device, although you can pair it without one.

    • DT

      you can use a wired connection, but that still will require a router. You just might already have one.