Most of the POS companies integrate a known biometric device into their own hardware / software. Most biometric device companies will offer some type of SDK to totally integrate the software to the hardware.
Problems with biometric devices:
1.
The more employees, the larger the recognition database = slower response.
2.
Color of skin, quality of fingerprint, etc has an affect on the accuracy or ability to recognize.
3.
Some POS companies will only load the recognition database of clocked-in employees, this is ok after they are clocked in to improve response time, but still sucks for employees first clocking in.
4.
If the recognition technology doesn't use some sort of fingerprint detection algorithm, but visual input only, then this can be easily fooled (Like use a pencil eraser on the optic in place of a fingerprint).
I've worked with several, and my fingerprint hardly ever works and some people's works fine every time. Unfortunately I have yet to find one that works well enough to install in a pilot location for a test. -It's getting better, just not quite there yet in my opinion.
