This is the best toy I have bought in a very long time. In short, you wear a silly looking headband during the night and the ZEO measures your sleep (deep sleep, light sleep, REM and wake phases) and also calculates a ZQ (sleep quotient). You then then enter some values for a number of so called sleep stealers, e.g. having exercises vigorously in the evening. Over time, their online software provides you with very good analyses about your sleep, factors that impact on good and poor sleep, and also effects it has during the next day. Here's a couple of screenshots and also a report from the first week of usage.