As well as being remarkably small, it's remarkably effective - they weren't exaggerating in those videos where they talk about how well it distinguishes movements. I was prepared for a slightly disconnected interaction with false positives but it's very accurate distinguishing unintentional moves from distinct swipes. It's also able to deal with the screen in both orientations. There's also a very subtle UI hint in the form of a glow along the top of the screen when the radar has seen your hand, which zips off to the right when it senses a proper swipe.

Whether they get enough engagement to take it out of gimmick territory is what interests me. They need to keep pushing it. Alarm snoozing is a particularly handy use but that, track skipping and face unlock need to be the start rather than the zenith.