This is a research project on myself actually. I'm already physically active, run half and full marathons, and am involved in dance and Ultimate Frisbee. BP is good and so is HR.
But I'd like to get a device that I can wear to bed, and the reason is that there is a point in time where I can "feel" my HR begin to drop and everything relax, and I'd like to punch a stopwatch off (and then just go to sleep), and then come back and compare the time start with the heart rate history and see how they correlate.