There is a switch to turn it off:

"There’s also a handy waterproof switch on the cap that lets you change from the white LED (bright), to red (preserves your night vision), or turn it off completely."

I hadn't seen that the batteries are rechargable--that makes it more attractive to me. I wonder if it'll run on NiMH batteries rather than NiCad. Hmmm... I'm sure the experts at Candlepowerforums would know about it.

I wonder if the cap/light fits a standard Nalgene. That would be cool.