I place my thumb on the display of a dummy smartphone. A tiny, imperceptible wave of pressure shoots out of the device and maps the ridges and valleys of my finger, verifying my identity.
In an instant, another phone that's connected to the dummy flickers to life as the home page appears.
I'm standing in a conference room in the heart of Qualcomm's San Diego headquarters, trying out an early -- and very rough -- prototype of the company's ultrasonic fingerprint reader, which Qualcomm says will show up in smartphones next spring.
The technology is the same as that teased by DJ Koh, the head of Samsung's mobile business, at an event in China this week. And while Qualcomm declined to comment on any specifics phones using the technology, and Samsung remains mum on what will show up in the Galaxy S10, any phone embracing ultrasonic waves to read a fingerprint will have to work with Qualcomm.
Embedding the fingerprint reader underneath the glass represents the next step in how we verify our identities and log in to our smartphones. It's also a convenient fit with the trend toward eliminating physical home buttons and enlarging the frame around the display. The more full-sized display has forced phone makers to move the reader to the back of the phone or, in Apple's iPhone X, gotten rid of it entirely in favor of a facial recognition system.
Putting the fingerprint reader under the display was once considered a holy grail technology -- largely because it failed to materialize after years of rumors. But they're starting to pop up: CNET got a look in January at a prototype Vivo phone with an in-display fingerprint reader, and Huawei has put a reader into its special-edition Porsche Design Huawei Mate RS phone.
Both the Vivo and Huawei phones use optical technology to scan the fingerprint through the display, a different technique than that employed by Qualcomm. Regardless of the technology, in-screen fingerprint readers are expected to show up in a big way next year. Consumer research firm IHS Markit predicts that 100 million phones will have in-screen fingerprint sensors by 2019.
How does it work?
Qualcomm uses sound waves to generate a map of your fingerprint, with the wave of pressure bouncing off the contours of your skin.
Ultrasonic technology offers a few advantages, said Gordon Thomas, director of product management for Qualcomm. It can read a finger even if it's wet, since the waves can pass through the liquid. He touts a 1 percent rejection rate, as well as a lag time of 250 milliseconds, comparable to traditional capacitive fingerprint readers on home buttons found on the iPhone 8 or the Galaxy S9.
The sensor itself is 0.15 millimeter, so it doesn't add much thickness to the phone. It can also work through glass or metal. In fact, a version of this technology is out there with the Huawei Honor 10, but the company chose to place the fingerprint reader in the glass chin below the display.
Last, the ultrasonic waves can also be used to track blood flow and heart rate.
The alternative in-screen optical readers are built by the likes of Synaptics and Goodix. Instead of sound, they use light waves to map the fingerprint, but they can be thrown off by different lighting conditions and by water. Goodix's technology powers the Mate RS, while Synaptics and Goodix are also in Vivo and Xiaomi phones.
"We already have reliable high-performing solutions in multiple smartphones at retail today," Synaptics spokesman David Hurd said in response to Qualcomm's suggestion that its technology is superior.
A spokesman for Goodix couldn't be reached for comment.
So where are ultrasonic smartphones?
Qualcomm introduced this fingerprint technology last June, but few smartphones have publicly embraced it.
That's because the ultrasonic waves will work only through flexible OLED displays, according to Gordon. Phones more commonly used what's known as rigid OLED, which has air gaps that prevent pressure waves from going through.
The Honor 10, for instance, had to place the reader in the glass section below because it wouldn't work through the display.
It's so difficult to obtain a flexible OLED display for a demo unit that Qualcomm doesn't even have a working prototype, which is why its engineers had to pair up a dummy phone with another smartphone for my demonstration.
Which brings us back to Samsung.
The Korean tech giant uses the right display technology, and could use another gee-whiz feature when touting its 10th anniversary Galaxy S smartphone.
Talk about making waves.
Correction at 8:15 a.m. PT: This story initially misstated the thickness of the sensor. It's also been updated to note that rigid OLED displays have air gaps.
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