What is the relative accuracy of the various methods of recording sleep (i.e. Phaser vs. smartwatch vs. sonar)? I am willing to invest a bit of money in a system that will accurately measure my sleep, but I do not know which is most accurate. I am also interested in the relative accuracy of each to assess cost/benefit - I am willing to pay $89 for the Phaser if it is 50% more accurate than the other two options but not if it is only 5% more accurate. Obviously, there are many variables that make quantifying this difficult, but even an educated guess would be appreciated.