My guess is that they decided to release the demo earlier instead of spending days/weeks getting up to speed with low-latency audio processing in the Android JNI.
It's an academic demo/press release. Not a software release for production/market.
To be completely honest, it's been a long time since I've messed with audio-stuff on the Java-side, so not sure if/how much things have changed for the better.
Last time I worked on Android Audio was around the 4.1-4.2 era, and it was absolutely brutal compared to iOS. Glad to see that it's improving finally!
A lot of researchers are more than happy to discuss their work, but a big part of the academic industry is your research's impact and references. A way to get a better handle on who is looking at or following on with your work is to implicitly ask them to have a conversation with you before getting the whole kit 'n caboodle.
I assume other academics are allowed to reimplement methods in order to reproduce the result and to compare to their own methods. Can I do the same as a learning exercise?
I think you mean "explicitly"
The researcher was happy to provide me with their test images to verify that my implementation worked. Try asking.
It's a neat idea, but without a dedicated component or an extremely high-speed RTOS, you're not going to come close to the level accuracy that's really needed to do the math and still allow interaction.
I don't mean to rain on the parade, but I just don't think they really have anything usable.
And I would expect latency for such heavy DSP work on a phone.
I'm not sure that's the purpose. I wouldn't think of this as being intended to be a fully usable product right now. They could be intending it merely as an interesting experiment to explore new possibilities for interaction with mobile and wearable tech.
Another CS student came up with a virtual keyboard using the iPhone's accelerometer. It only had ~80% accuracy, so was it all that useful or practical? Probably not. But could it lead to another person or company refining the technique for production in the future? Certainly.
 Video: https://vimeo.com/49780741
If it comes down to using something other than your fingers, someone has the nose working as a user input device:
Only so many times a company can say they've got their issues ironed out before I stop believing them.
Of course that would only be valid if you proceed to then steal the person's card right afterward, so all in all, not that useful.
Reminds me of SOLI (which is radar rather than sonar): https://www.youtube.com/watch?v=0QNiZfSsPc0
Is there a way of trying this out? I know it'd only be demo line drawing applications but it'd still be interesting to try.
But it's also worth keeping in mind this is all off-the-shelf hardware. It seems very likely to me that if a cell phone or smart watch was designed to do this from the get-go that several easy hardware improvements and maybe a bit of custom DSP work would make this work much better. (By "easy hardware improvements", I mean things like speakers intended to emit frequencies for sonar, microphone arrays intended to receive them, etc.) From that perspective, even if the system we saw is fundamentally limited I'd still call it incredibly promising considering the constraints it is operating under!
If I were a smart watch manufacturer I'd be falling over myself to get one of my best engineers and one of my best recruiters an appointment with these people.
Leap Motion made huge improvements a few weeks ago with their Orion SDK:
We must be close to actually getting something basic for our desktops.
Really? And your phone is on? With the screen visible for them to see what they are interacting with. And as they are fumbling around in your personal space inches from your hand or pocket, no one notices.
Get real! If true you should be more worried about pickpockets than some random gestures.
You know, check for what's the foreground process, notice it's a password manager or bank application (or even a lock screen would do, who knows, maybe user had reused the same PIN elsewhere), blast the speakers with ultrasound and wait for the typing-like movement patterns.
It's a really cool concept. I wish they'd open source what they have, or at least have plans to open source it. However if this came about via University funding, they'll probably claim IP on it. If it was a student's own fellowship, he/she/they might decide to create a start-up out of it.
I have the feeling, every few years someone has the idea again, to use ultrasound for something and it starts promising, but then the accuracy and lag doesn't go away and dogs and cats go wild.
if people really want this type of interaction then phones will start to incorporate specialized hardware for it.
Also, consider that your ear/brain apparatus estimates object positions and occlusions from audio signals all the time.
Also also, the eighteen-wheeler problem is vastly different from the finger problem, as the latter is smaller, slower, and closer to the microphone, each by 1-2 orders of magnitude.
To address your comment more directly, I don't see any information theory type limit immediately applicable here for finding xyz coordinates using echolocation. That's done in a variety of contexts.