Wall Street Journal‘s Joanna Stern slept with the Withings Aura, the ResMed S+, and a bunch of gadgets to find out to see if collecting data about sleep can lead to a more restful night.

“The sleep-cycle data you get from these are at best approximations,” said Lawrence J. Epstein, an instructor at the division of sleep medicine at the Harvard Medical School. “The information you get is most accurate in telling you how long you’ve slept and if you are following a good sleep pattern.”