A childhood belief about cars

I used to have a sports coupe with a pretty nice stereo system installed. There were small controls on the steering wheel that controlled the most common functions of the stereo, such as switching between the CD and the radio, changing CD tracks or channels, volume control, etc.. These controls allowed the driver to operate the stereo without taking his/her eyes off of the road.

I'm a computer programmer, and I duped my sister and two of her friends into thinking that I had reprogrammed the stereo into responding to my voice commands. I'd say something like "volume down" and then turn the stereo down using the steering wheel controls. When it wouldn't respond to their commands, I simply told them that the system only recognized my voice.

Imagine my sister's surprise when she got her driver's licence and borrowed my car...