Dien,

Just for the Fun of it, really interesting Quick example of exploring slightly deeper into related and other Money making ideas...

Amazingly! Huge industry... Just like so Many other Niche industries...

Truly Unlimited!!

Winding Automatic Watches by Hand - WatchCases.com
http://www.watchcases.com/winding-au...nd.html‎
With the growth in popularity of mechanical automatic watches there was developed a small market niche of consumers who needed/wanted to not have to ...

http://www.watchcases.com/vacheron-c...h-exhibit.html

And...

An In Depth Report On the History and Innovations of the Watch ...
http://people.timezone.com/library/a...s/archives0097
http://people.timezone.com/library/w...68591017665598

niche applications - e.g., radioactive batteries [81] can last for decades, but ..... the issue of mechanical power scavenging with the advent of the self-winding watch. ... Taking apart a modern self-winding wristwatch reveals a 2 gram “proof” ...
http://www.cc.gatech.edu/~thad/p/boo...lectronics.pdf

Thanks to the Good ol' internet...

Timeless ways to mechanical self-winding...

Specialized Niches and Endless business ideas...

Especially the [Untapped] re-workable, ''Concepts to Think about Getting into in a Unique kinda way!

All the best,
Phil