Traffic signal sensors are essentially metal detectors buried in the road surface. These "inductive loop" sensors are easy to spot because they have a circular, square, or diamond-shaped saw cut in the pavement just before the intersection. There is a weak radio frequency field over the coil, and a large inductive mass disturbs that field. Loop detectors are meant to pick up the presence of large masses of metal - like cars and trucks - sitting still over the detector loop.
Most modern bikes don't have enough inductive material in their frames to trip the sensor, and what they do have tends to be oriented vertically above the loop (making it harder to sense) so you get stuck at the red light.
The Green Light Trigger emits a wide and powerful magnetic field that when passed over a detector loop, disturbs the sensor loop's field, simulating the arrival of a much larger vehicle. When the control computer sees that signal, it knows someone's there, and the biker gets their turn at a green light, just like everyone else.