"Now suppose TiVo came out with a tiny, pen-shaped digital audio recorder. Once in your shirt pocket, it would continuously record the sound around you. At any time, while continuing to record, you could play back the last 20 minutes of whatever you've just heard: a co-worker's brilliant utterance, something you didn't quite catch on the car radio, or driving directions somebody rattled off too fast. (As on the real TiVo, it would continue recording even as it played back.)
Because it would always be on, you would never worry about missing something important. And no family argument would ever again devolve into, "But you said . . . " and, "No, that's not what I said!" "