Originally Posted by
CPH-Flyer
No transit security was there for a long while in Narita as a trial, then suddenly it was suspended for a brief while and then came back in both Narita and Haneda. There is a caveat which is if you get a bus gate, then transit security will be the name of the game.
So it's all on a trial maybe-maybe not basis, no explicit policy, and if you get a bus gate, you're hosed. So best not to expect security-free transit if coming from the US!