Infrared beams on the sides of the cabinet that track the player's hand height and motion in the air.
For the uninitiated, "Emuline" is a portmanteau of and Online . It represents the fan-driven effort to emulate Sega’s ALLS (Arcade Load and Lock System) hardware on a standard PC, allowing players to run the arcade version of Chunithm at home, complete with online leaderboards, friend lists, and event tracking.
The "Emuline" magic happens when the emulator connects to this private server. You are playing the exact arcade binary, not a "home port" or simplified version.