Robot umpires are coming to MLB. Here's how they work

Only active participants—specifically the batter, pitcher, or catcher—are permitted to initiate a challenge. This is performed by tapping one's helmet or cap, and any assistance from the dugout is strictly prohibited. Challenges must be executed within a narrow two-second window, after which the graphical representation of the pitch and the official strike zone appears on stadium scoreboards and broadcast feeds. The umpire then processes this data and announces the updated count to the crowd. During spring training, these efficient reviews averaged a remarkably quick 13.8 seconds.

What is the technology?