Funny you should mention this. Benn Jordan, on the heels of his Flock camera research, reverse engineered a non-flock ALRP unit and built his own system using some off the shelf parts, a tablet, and 3D printer. He did it mostly as an experiment but also due to the fact that Flock's algorithm for image detection is astoundingly bad and has a high incident of reading plates incorrectly.

There are a handful of open-source models for license plate detection, I forget exactly which model outperformed the rest, but it was an excellent watch and help me really understand just how inefficient these commercial systems are and how easy they can be to defeat: https://www.youtube.com/watch?v=Pp9MwZkHiMQ