Yeah, probably a few gyroscopes/accelerometers.

I would guess that it is a beefed up version of something like this: http://blog.makezine.com/2012/03/28/an-inexpensive-self-bala...

I like their tiny kickstand as a solution for keeping the thing upright without draining the battery. I wonder if that deploys only when the bot is in sleep mode, or if it can come out when someone is using it but "standing" in a single spot for a prolonged period of time.