I am going to be building a small 'monument' that will be intended to last thousands or more years. I would like to include some electronic/electrical appartus that will have a small power consumption when demanded (no power use until a button is pushed or something). My question is this (and I know there may be many reasonable answers)... What kind of power generating or power storage equipment could I build that would be the most simple and most reliable over a very long period of time. The power I would need would be less than 40 Watts instant demand, and probably 10 watts continuous for a few hours at a time. Of course more is better. Picture this example: Someone 10,000 years from now happens into a cave and finds a simple apparatus that intrigues them. Upon examination they realize there is a button to push and push it. This apparatus then displays some information to them in some manner. If they see it is broken, provided they are not the intellectual equivalent of a monkey, they may see what it is that needs to be set right and repair it. I don't want some device that is the size of a house or that requires materials that will definitely put me on some terrorism list (think uranium or plutonium). Simpler is better. Something that is easily repaired or replaced by someone that is intelligent yet unskilled would be nice. A voltaic pile would be really cool provided I could rely on it to function 10,000 years from now and that it would last an extremely long time. I know there are some still working today, but I really don't know what to expect of them over millenia ... However a very simple bike like or crank device that would power a small generator may be very workable, however, it would have to be of a design that was very robust and virtually indestructible. Solar is mostly out of the question unless someone knows of a glass that never needs cleaning and will remain unbroken over millenia. Anyone want to shoot me some good solid ideas?