AS608 Optical fingerprint reader module
This module does much more than just scanning fingerprints, it also processes the fingerprint and sends the processed data to a microcontroller via serial. Another function of this module is that all registered fingerprints are stored on this product. You can thus use even small microcontrollers with this unit as all hard work is done by this module itself.
All the microcontroller does is to receive the probability of the accuracy of a fingerprint, you then just have to program your microcontroller what to do, for example, open a door.
The Adafruit libraries and examples work great with this AS608 Optical fingerprint reader module.
Here is a link with lots of data: https://learn.adafruit.com/adafruit-optical-fingerprint-sensor