The iPhone X was supposed to be the first phone in the market that offered an under display fingerprint sensor. However, due to complications, the company could not deliver and replace the security method with a very advanced face recognition technology. Failure did not stop them, because they are coming back with a very different method to get the fingerprint sensor under the screen.
While Synaptics has managed to show their technology in both the Vivo X21 and the Vivo Apex, Qualcomm has been working hard to use ultrasound to read our fingers. This method does not use light or electricity, the ultrasonic sensor will be able to pass through the glass and make it easier to use with any type of phone glass and it will even work fine if your finger is wet or dirty. Downside of the ultrasonic sensor is that it is rather costly to and difficult to make, so we will only expect to see this type of sensor on flagship phones.
As of now, three companies are developing this sensor, Qualcomm, Apple and Samsung. However, seeing that the relationship between Qualcomm and Apple is not the most stable, Apple will probably develop their own type of ultrasonic sensor, which means Samsung and Qualcomm could be hard at work developing this sensor for the mass market, as they have a long ongoing relationship.