We've come to a conclusion about how to measure sleep! The process included research into what actually happens when you sleep. I found this other wearable sleep sensor made by students at MIT called Somnus Sleep Shirt (http://nyxdevices.com/product/) that measures sleep based on breathing and heart-rate. So, as it turns out, you can measure sleep using heart-rate! And that's great news for us because we will already be ordering a heart-rate monitor to measure exercise.