Over the past couple years we have watched smartphone manufacturers struggle with the placement of their fingerprint sensors. Some put them on the front of the devices where home buttons used to reside and others put them on the back. That latter option has become more common as smartphone design has moved to displays taking up the entire front of a phone leaving no room for physical buttons. The solution to that is a fingerprint sensor built into the display, a solution that has been more difficult to get to market than some may have thought. That may change with the unlikely release of the Vivo X20 Plus as the first smartphone with an in-display fingerprint sensor.