Now, obviously, engineers didn't develop cruise control to increase the odds of plowing into something. I tripped over some unintended consequences while traveling on an airplane during the Thanksgiving holiday. These headphones, made by Aiwa, sample ambient noises and pump out sound waves that exactly cancel them out. The technique is useful only with repetitive sounds, such as engine noise or the wash of white sound that comes out of an air-conditioning system. If you were to draw a picture of what's happening, each peak of surrounding noise would be met with a trough of a sound wave from the headphones, eradicating that particular sound but leaving all the other noise fully audible.
Many companies make such devices.
I just grabbed the Aiwa headphones because they were lying around the office, a handy byproduct of research for our holiday buying guide. Let me state up front that the Aiwa headphones worked flawlessly. I sat next to the engines on both legs of this trip, and with the headphones on, the jet became extraordinarily quiet. They were all talking over the sound of the engines, you see. There was one passenger 12 rows behind me who seemed to be genuinely mad.