Another health and fitness device from the Unveiled event. The Emfit Sleep Tracker is a bit of a misnomer because it does a lot more than tell you how much REM you've had in the night. Aimed at pro athletes or those just obsessed with their fitness, it also measures heart-rate variability, which shows how quickly you recover from exercise and whether your body's stressed from too many hours at the gym. It does all this with a long flat sensor that slips under the matress and detects the minutest compressions from each heart beats -- the only sensor that can measure heart rate variabiity without bodily contact, according to Emfit. It's on sale now for $299.