Once upon a time – and not so very long ago – if you wanted to understand how soundly you were sleeping, you needed to go to a lab for a specialized test. Known as a polysomnography, it would measure:

• Brain waves (EEG);
• Breathing, including how easily or not your breathe, how often you stop breathing and for how long;
• Heart rate and rhythm;
• The flow of air in and out of your lungs;
• Muscle activity;
• The positions you sleep in during the night;
• The movement of your eyes; and
• Oxygen levels in your blood

...all while you are sleeping.

Nowadays we have sleep tracking software built into wristwatches upon which we rely to report on how well we sleep. But is it reasonable to assume that some hundred dollar gadget strapped to your wrist can provide results comparable to all those electrodes clipped to your head and chest? The answer, now that you have stopped to think about it, is of course “no.” But just how far apart are the results, and just how much “sleep tracking” are you getting for your hundred bucks?

To appreciate the answer, it helps to first understand how your fitness tracker examines your sleep. The process of using the accelerometer in your watch to measure unconscious movement is called actigraphy. It is premised upon the notion that “X” amount of movement translates to being awake, and “Y” periods of motionlessness means you are asleep.

A 2011 study put actigraphy head-to-head with polysomnography, and deduced that wrist-based sleep-tracking was “useful” in estimating information such as total time asleep, sleep percentage, and how long after sleep waking occurs. Later studies concluded that the more disrupted your sleeping was in general, the less accurate overall was wrist actigraphy. But given their cost and convenience compared to polysomnography, gadget-based trackers were still a worthwhile investment for the sleep-curious.

More recent studies, however, are indicating that gadget-based sleep trackers are reinforcing poor sleep habits. Fans of the gadgets are awakening feeling refreshed, but the “data” is telling them they slept poorly. Consequently, they might spend more time in bed in an attempt to game up their sleep tally. Others who are not sleeping properly are not seeking proper help because the Dick Tracy dongle on their wrist tells them not to worry. It’s a symptom of our data-obsessed society that many of us believe our gadgets over our gut.

Psychologist Kelly Glazer Baron, PhD, MPH, who just published a new case series in the Journal of Clinical Sleep Medicine, cautions against “orthosomnia.” That’s her term for “the perfectionist quest to achieve perfect sleep.” She’s based it on the clinical term orthoexia, which is the similarly unhealthy preoccupation with healthy eating. As she summarized, “It’s not always possible to hack the perfect night of sleep.”