I am using the Dreem 2 (dreem.com, use my referral code for a discount: UEXBFMANU). I do not have a certified reference device but those aspects of the recordings that I can assess (start and end of sleep, awakenings, onset of sleep, position) match my experience and are more accurate than the other devices I am using (Withings Sleep, Garmin Fenix 3). There are several in depth reviews on the web comparing the device output with state of the art polysomnogram recordings.