High-pitched sound is making a comeback. Engineers have discovered that ultrasonics, which have been around almost as long as electronics of any sort, can give modern devices some cool, futuristic features.

Ultreo ultrasound toothbrush

Mankind has been capable of making high-frequency ultrasounds for at least a century. Today, we use them to clean our teeth, capture the first images of our smallest humans or improve our photography. Tomorrow, it looks like we’ll be using them to link our gadgets or control them with the wave of a hand.

Google announced its Chromecast TV streaming stick will pair ultrasonically with phones, so you won’t have to share Wi-Fi passwords with friends anymore. Elliptic Labs has figured out how to use ultrasounds to enable mid-air (read: touchless) control over our phones, tablets and laptops. It’s gesture control that actually seems to work well, and it’s heading to the market next year. And they’re not alone.

The Sweet Sound Of Hooking Up

Shopkick’s ultrasonic transmitter/speaker

At its bare bones, ultrasonic technology requires a speaker to emit sound and a microphone to pick it up. But not just any sound. These are audio waves that oscillate at a high frequency beyond the range of human hearing (20 kHz or higher). Nearby mobile gadgets and appliances, however, can hear them just fine.

That’s why companies like Shopkick and Clinkle pursued ultrasonics as a proximity technology for retail applications. Shopkick lets stores locate customers inside, so they could push promotions onto the phone tied to specific aisles or departments. (Later the company brought in Apple’s iBeacons, which does essentially the same thing over Bluetooth.) Clinkle hasn’t officially ditched its ultrasonic approach to payments, but it hasn’t publicly launched it either. (Perhaps it’s too busy dealing with the revolving door in its C-suite.)

Plenty of other companies, though, are trying out ultrasound controls in other realms—like our living rooms.

Google’s Chromecast TV streaming dongle, waiting to hum with ultrasonic pairing

The engineers behind the popular Chromecast streaming stick knew they had a hit on their hands, but they also knew it wasn’t perfect. Pals can’t just come over and start slinging streamed video to your television; first you have to dig up your Wi-Fi password, and then they manually punch it into their devices before your Chromecast party can get started.

To eliminate that first-world digital drudgery, Chromecast product manager Jagit Singh Chawla and his colleagues decided on ultrasonic pairing. It uses a sort of PIN code to connect devices directly, instead of over a Wi-Fi connection. The numbers get encoded into an ultrasound signal played by the TV over its speakers. The smartphone picks it up on the microphone and decodes it—no typing necessary.

In this case, ultrasound communication was a fitting solution. “It’s a universal technology,” Chawla said. “Most TVs have speakers, and phones have speakers and microphones.” So most devices already have the bare minimum hardware. Plus, the short range offers a limitation that, it turns out, actually improves security.

“All we need to do is to prove that you’re in the same room,” he said. “Ultrasonic being high frequency doesn’t travel too long.… There’s no way to take it outside.” In other words, your neighbors won’t be able to hijack your Chromecast from their easy chairs next door.

Next-Generation Gestures

When ultrasounds hit objects, the audio waves get disrupted or echo back. That’s how devices can detect when other things are in the way—much like bats, who echolocate using high-pitched squeaks.

In a rudimentary sense, that’s how ultrasound imaging works, by registering the feedback. It’s also the way Elliptic Labs can tell where your hands are when you’re gesturing near your tablet or smartphone.

Qualcomm’s ultrasound NotePad and pen

The use of ultrasound in mobile devices is not a new idea. Qualcomm’s purchase of Israeli ultrasound technology firm EPOS in 2012 led to the mobile chip maker unveiling ultrasonic pen technology at the 2014 Consumer Electronics Show. It’s an intriguing concept—partially because this souped-up alterna stylus doesn’t actually have to touch the screen (or NotePad) to work. A user could theoretically write on a piece of paper nearby, and those scrawls could register on the device anyway.

Mid-air gesture control isn’t new either. The Samsung Galaxy S4 and the Leap Motion controller both promise the same sort of alakazam! functionality that ties hand-waving to device actions. But those products use cameras to track movement, whereas Elliptic relies on ultrasonic waves.

The primary differences seem obvious. With no camera, there’s no field of view to limit the working range or sunlight to battle. Indeed, Elliptic’s gesture control—which uses a specialized high-resolution speaker—works in a 180-degree range around the device. And judging from this demo video, shot by TalkAndroid, it appears to be pretty accurate.

At only a 5x5x5 mm size, the tiny speaker can fit inside today’s mammoth smartphones, not to mention tablets and laptops; some gadgets may even be able to use their existing microphones. Ultimately, the cost for manufacturers can be quite low; the speakers don’t put much strain on precious battery life, either.

No wonder device makers have been beating down CEO Laila Danielsen’s door. “Every single OEM [original equipment manufacturer] is coming to us or talking to us,” she said. “There’s at least one that’s trying to do it themselves, which is good. But the rest are talking to us.” Among them was Amazon, which first contacted Elliptic Labs a year and a half ago.

Ultrasonic’s On Fire

Amazon CEO Jeff Bezos showing off Fire Phone’s Dynamic Perspective

Amazon’s Fire Phone, which just launched last week, now relies on four cameras for its Dynamic Perspective feature. But back then, it was exploring an alternative way to track user movement in front of the device, presumably so that it could deliver the 3D-like visuals based on their viewing angle.

“We were not ready,” said Danielsen, sounding a little disappointed. She had just joined the San Francisco and Oslo, Norway–based company, and it was in the process of shifting from a research to product focus. But that didn’t stop Elliptic Labs from scooping up one of the Fire Phone team members.

“One of the the key leads on this Dynamic Perspective project really believed in ultrasound,” she told me. “I told him that we weren’t ready for what you’re trying to do.” The product would’ve needed redesigning to work with the Fire Phone.

A glamour shot of the Amazon Fire Phone

“He said, ‘Ugh! I could do a much better job at this…. Let me know when I can join your team!’,” Danielsen said. “He joined in January.”

With the Amazon defector in tow, Elliptic Labs now seems to be in the catbird seat, cherry-picking partners that can move swiftly to get its technology into consumers’ hands. The company currently offers software development kits for Windows, Windows 8 and Android, and “we are building products as we speak for launch,” said the CEO, who also recently opened a Shanghai office to cater to Asian OEMs. “We are targeting the next 12 months, for products to come out on the market.”

Where could Elliptic’s technology show up next? Danielsen’s not sure yet, but she has a team “looking for longer term areas.” Possibilities range from connected health gadgets and wearables to smart homes and cars—anywhere people might want to control the action with the flick of a hand.

For now, though, Danielsen and her crew are focused on mobile devices. Which may be wise, considering momentum could be building there.

Samsung’s Ultrasonic Cover for its Galaxy Core Advance smartphone

Samsung hopped on the ultrasonic wave recently, debuting a new ultrasonic cover for its low-end Galaxy Core Advance smartphone. An assistive technology, the case was designed to detect the presence of physical obstacles. The South Korean tech company said it plans to expand accessibility of other Galaxy devices, which means ultrasounds could find a home in the Android maker’s other smartphones and phablets. It also filed a patent (.PDF) covering an ultrasonic stylus, not unlike Qualcomm’s invention, for its upcoming Note 4.

Samsung loves to experiment with features, and these moves strongly suggest that ultrasonics has become music to its ears.

Feature image by Flickr user Staffan Vilcans; Shopkick ultrasound transmitter image courtesy of Shopkick; Ultreo ultrasound toothbrush photo courtesy of Ultreo via Amazon; Qualcomm ultrasound pen image screencapped from Qualcomm YouTube demo video; Amazon Fire Phone images by Taylor Hatmaker for ReadWrite; Ultrasonic Cover photo courtesy of Samsung