It's not a video camera in the conventional sense, necessarily. You could also collect unfocused light emissions, such at those reflecting from walls and ceili

It's not a video camera in the conventional sense, necessarily. You could also collect unfocused light emissions, such at those reflecting from walls and ceiling, and correlate their luminance and chroma fluctuations over time with those of live TV. This would not intelligibly perceive non TV light signals, and so be less of a privacy concern. Additionally this would work if the TV's image is not visible.