The original jawbone Up bracelet thingy did that, and I LOVED it. Sadly they broke easily and Aliph (now Jawbone) stopped making them. I had an original pebbl

The original jawbone Up bracelet thingy did that, and I LOVED it. Sadly they broke easily and Aliph (now Jawbone) stopped making them. I had an original pebble, and kept hoping for a feature like that but it never came (or came after I stopped wearing the pebble). I've used Sleep Cycle on my iPhone for this, but it's not as accurate- especially with 2 people in the bed. Long/short is that to this day is still haven't found anything as good as the Up, which Was near perfect when it wasn't physically broken.