Perhaps it’s already clear to my readers from the number of articles I have written on sleep that I’ve been trying to find my way through this “hall of mirrors” of my life for a long time. Since the times of diapers; or maybe it would be better to say since the times of sleeping in sleeping bags. I will never forget the constant waking up, the long hesitation, the childhood fear, the chill in the air and the silent envy that the others were still asleep — in summer camps and on trips, when I had to leave the warmth of my sleeping bag several times a night to go out and pee somewhere in the dark. It’s still a familiar feeling up to today, only I’m just worrying about what the next day will be like, not about wild boars.:) Sleep is extremely important, it’s the pillar on which our physical and mental performance depends, our health, regeneration, metabolism, the speed at which we age…

And yet, as Professor Matthew Walker says, 80% of people in the West are suffering from sleep deprivation today. According to the number of grim stories of tired friends and loved ones who boast on the one hand that they “don’t need to sleep more than 6 hours”, and at the same are putting on weight or have various chronic health problems, I would say that his estimate is still conservative. Further proof of this can be seen not only in the extraordinary success and response to Walker’s bestselling book Why We Sleep (+ the buzz around it), but also by the growing number of gadgets and apps that have been developed to measure, evaluate and even influence sleep.

In this fairly lengthy text, I want to present the results of a month-by-month comparison of several state-of-the-art sleep screening devices (I refer to them simply as sleep trackers) that are intended to be used at home.

REM, NREM and Everything Around Them

First of all, let’s recapitulate the terminology and some basic facts. Healthy sleep has a typical multi-stage architecture. These are NREM1 to NREM4 (NREM1 and NREM2 are light sleep, NREM3 and NREM 4 range from deep sleep to very deep sleep) as well as the REM phase. These cycles take turns after about 90 minutes and cleverly follow each other. The rest of the night is filled with wakefulness. The time from switching off the lights to falling asleep is referred to as latency.

Sleep is initiated by at least two major processes: fatigue (sleep pressure, the adenosine cycle) and the excretion of melatonin into the blood (the Circadian rhythm). These two cycles should be in sync with each other. If they diverge regularly, for example, if you don’t have enough melatonin in your blood before falling asleep, problems will start to accumulate. Initially, they will be creeping and manageable and probably not attributable to insufficient sleep, but these will grow into chronic health problems over years and decades.

But for sleep to be sleep, and not to just be some state of unconsciousness, and for it to perform a variety of healing and key functions for the body and brain, it must be preceded by a prelude throughout the entire day and must have the right timing and length. When it comes to assessing the quality of it, it is not just about length, but about the depth and quality of each phase.

Plenty of people say that they “have no problem falling asleep in front of the television,” unfortunately this is a bad sign; they are falling asleep in a bad place. If you spend your days in an office under fluorescent lights and your evening glued to a screen until the final moment, it is true that you fall asleep because of being tired, however you won’t be able to rest at night (due to the lack of melatonin through which our internal organs typically recognize that it is night and time to rest). Along the same lines, the idea of “healthy drunk sleep” is a myth, because drinking alcohol is not about getting high-quality sleep and the brain and body are not able to regenerate, just getting by in a kind of unconscious state. Of course, this isn’t only about alcohol — caffeine, various foods, our level of hydration, the (ir)regularity of lying down and getting up, exposure to and lack of exposure to different types and intensities of light throughout the day, physical activity, health problems, medicine, smoking, etc. can also have a similar negative effect on our ability to sleep. All these circumstances affect the phases, depth and overall architecture of our sleep.

We, the sleep tinkerers, have already known this for quite some time. We try, often in quite an amateur way, to get the particular phases and the quality of sleep during them a little bit more under control or to at least measure them and look for “correlations”, or possible connections, to track the relationship between our lifestyle on the one hand and the quality of sleep on the other. I’ve been trying to do this for years myself, since I discovered the first gadget that promised to measure sleep in 2010 — called Wakemate — which completely fascinated me. Unfortunately, it didn’t work very well, and this endeavor later went on to languish, like so many other similar projects that promised to work like magic.

How Sleep Is Measured in a Sleep Lab

A professional sleep laboratory uses a so-called polysomnographer to scan several (12 or more) bits of biometric data from someone while they are sleeping, the main ones being: EEG (brain waves), ECG (heart activity), EOG (measurement of eye movement), and EMG (muscle activation), as well as the level of blood oxygen saturation and more. The different secondary quantities are then derived from these directly measured values ​​and the result is a polysomnogram which shows dozens of values ​​that can be used by the sleep expert for comparison and evaluation.

A polysomnogram — above you can see the brain waves, then below the other metrics. Source: Wikipedia.

On the basis of these metrics, the individual pieces of sleep are then evaluated and, among other things, a hypnogram is created, i.e. a graph of the night’s progress with estimates about each phase and other sleep parameters. However, the key variables monitored by the experts include brain waves measured using electrodes on the head (EEG) — without them, they cannot and aren’t intending to conduct a professional evaluation.

A hypnogram is the result of the polysomnogram being interpreted by an expert (the polysomnogram shown above does not correspond to this hypnogram). Source: Why We Sleep by Matthew Walker, Simon & Schuster, 2017.

You may suspect that ordinary sleep trackers (a smartphone under the pillow, bracelets, watches, a mat under the bedsheets, etc.) that are not able to measure any of the primary variables, rely on secondary or derived phenomena (sleep movements/actigraphy, heart rate, HRV) and determine sleep phases through a so-called heuristic technique. These are guesstimates. In other words, they speak inaccurately and often inconsistently about the stages of sleep, because the heuristic here is based on only a few pieces of (secondary) biometric data and therefore is more prone to bias by circumstances (e.g. the age of the sleeper, their long-term, as well as acute, health conditions, etc.). It should be said that the manufacturers of many gadgets and applications indirectly acknowledge this deficiency by calling the phases of sleep only “light sleep,” “deep sleep,” and “awake”. If anyone says their gadget or even app identifies your REM, NREM (or its sub-phases), be on guard. Without an EEG it will not work, as I will show in the comparison at the end of the article.

If anyone says their gadget or even app identifies your REM, NREM, be on guard.

Nevertheless, I think that even relatively inaccurate data can be used as a sort of orientation, as a rough guide and gateway to the world of self-measurement and sleep-hacking. The majority of apps for basic sleep tracking moreover will also force you manually adjust the time when you fall sleep and wake up, so that if nothing else, you can completely keep track with the app of the exact time you fall asleep and wake up, that is, the so-called sleep opportunity. Thanks to these records, complete with a simple rating for the night and the next day, you can develop a better awareness and be more motivated to work on your sleep habits. Gradually, your interest in having more accurate data and information will grow, or perhaps you will quickly come to the conclusion that it is better to go to a doctor. If, despite all your efforts and without a known cause, you suffer from severe insomnia or excessive fatigue during the day, a sleep laboratory could be the answer. I have been on the verge of going there lately…

A Short Anecdote — or How I Doubled My Amount of Deep Sleep

The following story is important because through it I want to show you how difficult it is — even with the greatest amount of effort, looking into quality resources and racking up considerable expenses on measurements — to find the origin of one’s sleep problems. From last December to March of this year, my sleep was terrible. Every morning, without exception, I felt drowsy and had brain-fog, and without a good cup of coffee and tea I couldn’t function. I planned my days so that I could take a short nap in the afternoon and refresh myself at home or at work (where we have the opportunity to do so). A midday nap is probably good for the heart, but it shouldn’t be something that you feel the need for every day or that you wouldn’t survive the afternoon without it.

I had already gotten fed up with these complaints and the constant analysis of the causes was annoying to me and the people around me, but — as I can see today — the overall quality of my life was really falling. At night, everything was wrong, according to Oura (I have my reservations about the accuracy of its measurements, but I will describe this further in the review below), and also according to my subjective “memories of the night.” I was waking up more and more at night, went to the toilet 3 to 4 times per night, couldn’t get up in the morning, etc.

Although this “insomnia campaign” has happened to me in the spring for a number of years, it had never lasted for weeks and nor had such intensity. It was only one night in April after which I forgot to make coffee and my head was running at 100% performance all day long, that I began to have hope that normal life still existed somewhere. I tried to remind myself of everything I had done differently in the days and evenings better than before.