From the Telegraph interview with Tim Cook:
I think we all suspected this but were still unsure because it's inductive charging. So maybe if charging times aren't that long one can charge it at night before they go to bed and then wear it to bed to track their sleep or use as a silent alarm. Jony Ive did say someone on his team was using it as an alarm.
The watch's battery life will last the whole day, Cook says, in another revelation that will please potential users, and it won't take as long to charge as an iPhone.
I think we all suspected this but were still unsure because it's inductive charging. So maybe if charging times aren't that long one can charge it at night before they go to bed and then wear it to bed to track their sleep or use as a silent alarm. Jony Ive did say someone on his team was using it as an alarm.