tap water power!
Ok, I couldn’t help myself.
I found something totally cool for $12. and it’s useful, not always the case for me. This crazy little clock which you can find at: http://www.realgoods.com runs on a tiny bit of water. One fill lasts it about two months. Great for places where you can’t expect to get enough light to charge a solar battery.
Size: 1.5“H x 3“W x 3.4“D