I’ve had quite a few inventive ideas: One in July 2003 was a recycling shower: a shower which filters and reheats the drain water from a shower, so once you’ve soaped and are clean, you can stay under a flood of fresh hot water as long as you like for very little heat cost, and no water cost. A second the same year was a pocket Wi-fi detector: a device which would tell you if there was a wi-fi connection near by.
Of course, both of these have become commercial items now. So… the lesson: if you want to make some money out of ideas: do something about it NOW. Sell it to someone who can protect and develop the idea, or, if you love it, build it yourself.