It isn't caused by any specific humidity levels. While it is depositing water droplets on to the glass surface, that same water is normally suspended harmlessly in the air (it is effectively de-humidifying the air onto the cold windows).
It is caused by the glass's surface temperature being much lower than the air temperature inside the car. Humans are warm. The air we breath is warm. We're heating up the interior of the vehicle. When that warm air contacts the cold surface of the glass, the water droplets migrate from the air onto the surface.
In order to detect it you'd need to know the glass's surface temperature ideally in the middle (away from the car's body) and also know the interior temperature. The interior temp they already have. But figuring out the glass's temp is non-trivial. Infrared camera is the only thing I can imagine working (since a sensor wouldn't be transparent or wouldn't be replaced when the glass is) but that would likely give inaccurate readings due to the outside temperature.
It is caused by the glass's surface temperature being much lower than the air temperature inside the car. Humans are warm. The air we breath is warm. We're heating up the interior of the vehicle. When that warm air contacts the cold surface of the glass, the water droplets migrate from the air onto the surface.
In order to detect it you'd need to know the glass's surface temperature ideally in the middle (away from the car's body) and also know the interior temperature. The interior temp they already have. But figuring out the glass's temp is non-trivial. Infrared camera is the only thing I can imagine working (since a sensor wouldn't be transparent or wouldn't be replaced when the glass is) but that would likely give inaccurate readings due to the outside temperature.