Okay, that ad got my attention...
In spam e-mail, an ad from Hammacher-Schlemmer, showing a small model rocket:
NEW. Our Safe Hydrogen-Powered Rocket blasts 200 feet in the air on clean burning hydrogen fuel crystals (just add water). Safety features assure a vertical ignition at a safe distance of 15 feet.
Hydrogen fuel crystals? Just add water? WTF?
A quick click on the web page. Oh, never mind. electrolysis, with some kind of electrolyte to speed the process.
Still kind of cool, though.