Even though it was Xiaomi who got to use Qualcomm's previous-gen "Sense ID" solution on its Mi 5s, this time the chip maker is letting Vivo get first dibs. Over at Vivo's booth, I got to play with a prototype -- based on the existing Xplay6 -- fitted with Qualcomm's under-display fingerprint scanner. The demo started off with a familiar fingerprint registration process, except I had to place my finger on a marked area on the screen, which was just above the old fingerprint button. Once done, I was able to unlock the phone by touching that same spot using my registered finger; and just to be sure, I tried with my other fingers which fortunately failed to unlock the device.

While the solution seemed to work as advertised, I found the fingerprint recognition speed to be noticeably slower -- about one second between first touch and entering home screen -- than the near-instantaneous unlock that I'm used to on most recent smartphones. I was also slightly disappointed by how small the recognition area was. That said, Vivo's demonstrators told me that in theory, the same sensing technology could be applied across the entire screen, but that would significantly increase production cost; instead, Vivo might eventually cover just the bottom half of the screen, which would still be better than what the demo offered.

In another demo, the company applied the same ultrasonic tech to a spot on the back of the phone's metallic body, thus allowing the phone to be unlocked even when placed in water. Since this unlock method could be associated with the camera app, this could come in handy for those moments when you want to take underwater photos or videos while in shallow water. But of course, other companies have solved this use case with a physical shutter button (Sony) or squeeze detection (HTC).

The Vivo reps couldn't provide a timeline as to when we'll start seeing this tech on their devices, but according to Qualcomm, its solution will come in two waves. "Qualcomm Fingerprint Sensors for Glass and Metal" can be integrated into devices powered by Snapdragon 660 and 630, and it'll start shipping to OEMs this month. As for the more advanced "Qualcomm Fingerprint Sensors for Display," it'll work with future Snapdragon platforms as well as non-Snapdragon platforms, and it'll only start commercial sampling in Q4 this year.