Omron's HT-B551 is the first electric toothbrush with a built-in accelerometer — the same tech that enables your iPhone to know when you're holding it upright or sideways. How does that help your teeth? Simple: If the brush is being held face-down, it knows you're cleaning the surface of your molar and can safely crank the vibration speed. Turn it sideways, and it'll slow down to make sure your sensitive gums get the gentle treatment.
Besides just speed, the accelerometer also controls bristle motion. They can vibrate vertically to get in between teeth in surface pockets, but horizontally on the sides of teeth. This seems like a good idea for a product — at least for people who don't tilt their head much when brushing. It's coming July 1 for about $200, but only in Japan.