Can I have my vaporizer in my carry on?

I'm curious if vaporizers(e-cigs) are allowed in carry on luggage.

I will soon fly from USA to Beijing. I know that vaporizers are legal in both countries. The only airport restriction I can think of is the liquids rule. But the liquid in my vaporizer doesn't even come close.

I've actually flown twice (domestic) and kept my vaporizer in my carry on. But maybe they just didn't notice it when I went through security.

I can't think of any specific reasons why these wouldn't be allowed, but I can't imagine that they are.