Watch the water level move on the screen as the phone moves! It drops as your battery level go down.

NTT DoCoMo in Japan just started selling the N702is 3G cell phone to its subscribers. The phone has a built in motion sensor. When the screen saver is activated, the screen displays glass-like water. The "water" moves when you move the phone around. The water level also reflects your current battery status, the lower it reaches, the less power you have.