British inventor and self-described 'eco geek' Pete Hopton and his company, VeryPC, have come up with a piece of eco-friendly software, PecoBOO, that uses an open-source face-detection program and your PC's webcam to tell when you're looking at your screen and, more importantly, when you're not.
When you look away for more than a few seconds, get up or generally ignore your screen, it'll turn off. Then, when you face it again, it turns on. This reduces backlight power consumption and, thus, overall energy consumption. As a result, you should not only get longer battery life from your laptop but could also save money.
The general idea isn't new -- other devices, like the iPhone, sport similar technology. The iPhone's optic sensor disables the touchscreen and backlight when you put the phone to your ear. PecoBoo is a natural progression of the same idea, although the end result is different.
Unfortunately, PecoBOO is currently available for Windows Vista and XP platforms only.