Thinking outside the box.
I saw a great example of identifying user needs and then finding a way to deliver them. There is a company designing tombstones with solar powered video monitors. You can record a memorial or testimonial video to your loved one, and store it in perpetuity on the tombstone.
It is solar powered, because of course you don't want to have to go periodically and put in new batteries.
It has an earphone jack, but no external volume. This way, you can listen if you want to, but there is no way to disturb anyone at (in?) nearby graves. Of course, you have to remember to bring headphones. If you don't know the video is there, you may lose out on the opportunity. But I have a sense that in another few years, we will all have headphones for our cell phone/PDA/music player combos anyway.
From what I could tell, there are either no controls at all (continuous looping) or there is just a start button and nothing else. This is probably better because it would really waste the solar infrastructure to have continuous loop for something that is only viewed a few minutes every long while.