Vivo has made the first phone with a fingerprint sensor built directly into the display. While it brings some practical benefit, the solution itself is a clever use of technology.

While fingerprint unlocks are relatively common now, they usually come at the expense of screen size. It’s not simply a case of effectively lopping off an inch of potential screen space, but manufacturers then have to decide between having a much smaller screen at the same aspect ratio, switching to an unusual screen shape, or making the phone itself bigger (and an odd shape) to maintain the screen size.

Reading a fingerprint through a display was an obvious solution, but until now it’s proved elusive, with both Apple and Samsung releases missing the feature despite rumors it was on the way.

Now Vivo has demonstrated a handset with the feature at CES and the key is through an OLED display. While phone displays look like a continuous image to the human eye, they actually have tiny gaps between pixels. These gaps are big enough that the sensors can ‘peer through’ and pick up enough points from the finger to distinguish the unique pattern of a fingerprint.

This approach wouldn’t work with an LCD display as either the backlighting would be on top of the sensor, blocking its view, or the sensor would be on top the backlighting, distorting the display.

When you put your fingertip on the relevant section of the screen (while the phone is locked), the display goes completely dark other than lighting up the area ‘underneath’ your finger, ensuring the best possible image for the sensor.

Those who’ve tried it out say it works smoothly: there’s a noticeable delay compared to the near-instantaneous fingerprint recognition on other phones, but not one that would be problematic or frustrating.