Just yesterday Google announced that it would soon allow users to send video and other entertainment items to a nearby Chromecast even when they're not connected to the same WiFi network, with the backend relying on location data for verification. It looks like there's some even more interesting technology going on behind the scenes. GigaOm reports that the upcoming update will allow Chromecast and Android devices to authenticate each other using ultrasonic waves.


Here's how it works. You're at a friend's house, and you've just got to show him the latest Honest Trailers video. If his Chromecast has the upcoming "nearby devices" option enabled, you won't need to get on his WiFi. Just cast from the app as normal, and the Chromecast will emit a series of noises from the television speakers that are above the human audible range. The phone will "hear" these sounds and verify the Chromecast, make the connection over the mobile network, after which the device will stream directly from the home WiFi. The Android user should still be able to pause, advance, and what have you from the phone or tablet. There's no reason this functionality couldn't also be added to other Cast-enabled devices.

Keen observers will recall that Google acquired SlickLogin back in February. This startup used phones as authentication tokens for logging in to websites on a standard desktop web browser, with extensions that authenticated the user with the same ultrasonic sound waves verified by the phone. Google didn't mention this particular acquisition when talking about the upcoming Chromecast feature, but it's a safe bet that some of the talent and/or tech went into it.

Source: GigaOM

Michael Crider
Michael is a native Texan and a former graphic designer. He's been covering technology in general and Android in particular since 2011. His interests include folk music, football, science fiction, and salsa verde, in no particular order.

  • Zyre

    Funny how they used the Nexus 4 model instead of the Nexus 5.

    • Matthew

      Nexus 4 was more popular.
      I think

      • Krzysztof Jozwik

        I've actually seen 2 Nexus 5's in the wild, the only 4's I've seen were the ones I recommended to people.

        • Matthew

          Nexus'es are for hipsters ;)
          Or geeks :P

          • Brad

            or for people who like having the latest android. oh... geeks. damn.

        • Roh_Mish

          I am now days seeing nexus 4 literally everywhere.

        • Brad

          I know of 3 within my friends alone... not to mention random strangers.

      • nebula

        I have both and I think, that the Nexus 4 is also more beautiful.

  • Kurt Schultz

    Pretty awesome!

  • Sean

    NOW we're living in the future.

    • Marla William


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  • Crispin Swickard

    And any dog in the room at the time will freak the f*ck out.

    • SHunter

      Because nobody thought of this...

  • Js__

    Well thats cool as shit!

  • Jesse

    This is very cool. However, I'm a little confused. How does the Chromecast know what video is being cast from the device not connected to WiFi? How would the Chromecast connect with the mobile network exactly?

    • Nathan Borup

      Chromecast has a mac address, or at least knows its routing across the internet. It probably emits the sound with that information

      • Jesse

        And how does that enable it to get the information of the video to be cast?

        • Nathan Borup

          the phone sends a signal with the information to the address given and the chromecast connects to the video. I'm only guessing here. It makes sense to me. You have to understand the internet

          • Jesse

            Ohhh I feel ya now, I think. So it's less like a direct connection between the two devices and more like them meeting at a third "place" somewhere on the Internet.

          • http://turbofool.com Jarrett Lennon Kaufman

            Which is nearly how it worked all along, anyway. You were always just sending it a command to then fetch the data itself. Now you're sending Google a command to send it a command to fetch the data itself. One extra hop.

          • Simon Belmont

            Exactly. You aren't actually on the network with the non-connected device.

            It's literally just authenticating that it exists in the same room and then telling it to signal Google to signal the Chromecast to get the right video. Awesome stuff that feels really future-y.

          • shajumohamed

            I still do't unserstand.
            How would the device know that I am trying to cast something?
            Will the chromecast be alway transmitting the information the auth info.

          • Nathan Borup

            It doesn't... your phone will recognize that it is near a chromecast because of the ultrasonic sound emitted from the TV, and then your cast button will appear

    • http://www.bordersweather.co.uk/ Andy J

      The fact that the user can still control play/pause etc without being directly connected to the Chromecast means it'll be a case of the Chromecast connecting to a server at Google to receive push messages - much like how Push Messaging works on Chrome and Android. So phone tells Google "send this message to the Chromecast" and Google passes the message on to the Chromecast, Chromecast then replies and Google passes the reply back to the mobile device.

      • Duncan Booth

        That still leaves a bit of a bootstrap question over how the phone knows which is the nearest chromecast in the first place. Presumably it has to start by making all Chromecasts on any visible wifi send out some ultrasonic pings and working on whichever responses it was able to hear.

  • Simon Belmont

    That's really cool technology. I have to say that the Chromecasts I bought have been the most useful and well enjoyed things I've ever got on day one from Google (outside my N5).

    I'm really pleased to see Google continue to give the Chromecast a lot of attention and expand its feature set. Good job, Google.

  • Braden Abbott

    This is exactly what I thought they would use when it was announced at the keynote, then I thought, nawwww

  • RedPandaAlex

    That makes sense. When I saw the demo, I thought it was some combination of location tracking, wifi signal strength, and voodoo.


    Uh, yeah, well whenever you notice something like that.. a wizard did it.

    • Random

      The wizard will now configure your software...

  • https://google.com/+LateefAlabiOki Lateef Alabi-Oki

    This is witchery.

  • Grahaman27

    Also note that android L uses the same technology for the "trusted devices" feature.

  • letsplaay

    Are TVs capable of blasting ultrasound by default?

    • Alphajoe

      Good question. I think most speakers will be capable to reproduce frequencies up to a range of around 17-20 kHz. The problem is, that young people and animals can still hear sounds in this range. Higher frequencies become unhearable even for young ears. But most speakers - except for quality hifi speakers (I know of tweeters which can go as high as 50 kHz) - won't be able to reproduce such frequencies.

  • Rg

    This feature can be a great troll! Can randomly connect to strangers Chromecast and cast some Porno.

  • Bob

    Hope the TV will not "advise" me directly in my head teling me what's my friend favorites genres..

  • strauzo

    Well we can still this ultrasonix wave to focse a phone to connect to our portable hotspot and sniff traffic :) INSECURE

    • Björn Lundén

      The data it will send is seemingly very limited. It also doesn't make the phone "connect to your hotspot". The data (what video to play and remote control) is still sent over the phone's 3G/4G connection.

      • strauzo

        I mean:
        that someone can use the new ultrasonic auto-pairing functionality to force a phone to connect to our hotspost to sniff normal daily internet traffic. not the traffic the the phone send to chromecast. (this is unuseful :) )
        the ultrasound can be recorder and played.

        if the phone and chromecast not establish a point to point connection this is another story. and and I did not understand the use.

        • Björn Lundén

          The ultrasonic signal is only used to let the devices to find each other. The phone never connects directly to the Chromecast but rather uses it's normal internet connection to send the data via Google instead of using the local Wifi network.