https://www.theverge.com/circuitbreaker/2018/6/11/17448214/vivo-x21-ud-in-display-fingerprint-sensor-review

After years of rumors and prototypes, an in-display fingerprint scanner is finally shipping in a major phone from a major company. The international Vivo X21 marks the first time this technology has been sold in India and other countries, as well as the first time it’s been a standard feature anywhere in the world.

In-display fingerprint scanners allow for smartphones with thin bezels and high screen-to-body ratios by integrating biometric authentication into the display itself. You could just put the scanner on the back of the phone, of course, as companies like Samsung, Google, and LG have done for years, but that’s less convenient in many situations.