In-display fingerprint sensors aren't strictly speaking new: Vivo launched the world's first phone with one in early 2018, and OnePlus recently brought a similar technology to the United States in its new 6T flagship. In our experience, they're, uh, pretty hit-or-miss. Most of the in-screen sensors we've seen shine light on the underside of your finger and visually check your fingerprint against a pattern it stored previously. This process will certainly get the job done, but it's a long way from ideal. Let's say you just had lunch — if your fingers aren't clean, there's a decent chance the sensor won't recognize you. And beyond that, it's at least theoretically possible to spoof that sensor with an image of the correct fingerprint.
Qualcomm's approach is /a little/ different. Rather than just store a flat image of your thumb pressed up against the screen, the company's sonic sensor uses sound waves to build a three-dimensional mold of your finger. Because it doesn't rely on visual data, Qualcomm's sensor should be much better at recognizing your fingerprints even if they're slathered in post-lunch schmutz. And since it's meant to capture a full mold of your finger — right down to the ridges and pores — the possibility of fooling this kind of sonic sensor is dramatically smaller.
So yeah, on a fundamental level, Qualcomm's sound-based approach to fingerprint scanning seems like a big step forward from some of the attempts we've already tested. That said, since we haven't actually tried one of these things yet, it's difficult to tell how fast a sensor like this would actually work. That might not sound like a big deal, but let's face it — traditional embedded fingerprint sensors have gotten staggeringly fast and accurate over the years, to the point where in-display sensors like the OnePlus 6T's can feel clumsy by comparison. Those milliseconds matter, and hopefully, we'll get a better sense of how well Qualcomm's ultrasonic sensor works before we have to leave Hawaii.