What’s the point of sleep? It’s a mystery that has baffled humans for thousands of years. The great inventor Thomas Edison, famously claimed sleep was “a criminal waste of time”. 21st century science, however suggests he was wrong. Sleep, it turns out, is far from a passive activity. Cell repair, hormone regulation, and vital brain functions are carried out every night whilst we snooze. Research suggests sleep is a vital pillar of health, as important as diet and exercise.
So it’s not surprising that to learn that lack of sleep is associated with a higher risk of many chronic health conditions. These include heart-disease, diabetes, cancer, and even Alzheimer’s. Such discoveries, coupled with the recent trend in wearable fitness gadgets have paved the way for a new wave of consumer health technology, personal sleep tracking gadgets.
How do sleep trackers work?
The gold standard for analysing your sleep behaviour is a medical procedure known as polysomnography (PSG). This entails spending a night in sleep clinic with dozens of wires and electrodes attached to your body. Whilst PSG gives you an unprecedented level of detail, it’s expensive and not particularly conducive to a good night’s rest.
So if you don’t need such an in-depth medical diagnosis, a technique called actigraphy is a simpler, more convenient way to gather long-term sleep data in the comfort of your own bed. Medical actigraphy, usually undertaken with wristwatch-like devices, has been used for decades to study sleep behaviour, as a supplement to PSG data.
Actigraphy uses a small electronic component called an accelerometer to measure your activity and rest cycles. Measuring only a few millimetres across, accelerometers are ubiquitous these days, found in everything from smartphones to washing machines.
In recent years, actigraph technology has broken into the mainstream. Piggy-backing off the quantified self movement, companies like Fitbit, Jawbone and Nike have created a multi-billion dollar industry by selling wearable devices that monitor and track your body activity and fitness levels.
It’s a small leap from activity tracking to sleep monitoring. The most basic sleep trackers, instead of measuring activity, monitor inactivity - or lack of movement, and use this as a proxy to calculate your sleep time. Obviously this can be prone to error. Your fitness tracker might interpret couch-potato Netflix sessions as a sleep period, when in fact you were just be relaxing.
Fortunately, sleep tracking devices are getting better at detecting sleep from wakefulness. Higher end devices include automatic sleep tracking, sophisticated algorithms and additional biometric sensors to measure not just movement, but also heart-rate, breathing, body temperature, and even your brain-waves.
Types of sleep trackers
For someone starting out in the world of sleep tracking it can be a little daunting to consider all the available options. So here’s a breakdown of the 3 main types of sleep trackers you’ll come across.
Sleep tracking apps
The easiest and cheapest way to start tracking your sleep is with a smartphone-based app. There are loads available for both iOS and Android phones, and many are free apps. Some of the most popular include SleepCycle, SleepBot, Sleep As Android. But because they all offer slightly different feature sets it’s worth trying out a few different ones.
Broadly speaking, all sleep tracking apps work in the same way. At night you place your phone in bed, or under your pillow, and then the phone’s built-in accelerometer detects how much you move at night. An algorithm then uses this data to predict a ‘sleep score’ - a prediction of how well you slept.
Sleep tracking apps come under a lot of criticism for their accuracy, however a lot of this has to do with experimentation and where you place the phone in bed. Of course, a free phone app will never give you the insights of a night spent in a sleep lab, but all taken into account, sleep tracking apps are a great way to get some basic insights into your sleep habits.
Wearable technology is big business. Fitbit sold 11 million activity trackers in 2015 and the trend doesn’t look like it’s going to stop soon. Most wearable fitness devices these days include some type of sleep tracking functionality.
Although basic trackers, like the cheap, but million-selling Xiaomi Mi Band only offer movement-based measurements, newer devices are continually upping the stakes in the biometric sensor departments. Devices like the Fibit Charge HR and Basis Peak are a hybrid between fitness bracelet and smartwatch, but with sensors that can monitor heart-rate, and skin temperature, their algorithms can perform much more advanced sleep analysis, and hence more accuracy.
As well as wrist-worn wearables, new form-factors are beginning to emerge. Oura, launched in 2015, is a ‘wellness computer’ that’s worn a ring on the finger. It’s makers have a strong pedigree in bio-sensor technology, having years of experience in designing heart-rate monitors for Polar.
Kokoon, is another intriguing product for those interested in sleep tracking. It’s a pair of headphones incorporating electroencephalography (EEG) sensors which measure your brainwaves. EEG measurements are one of the key metrics that define accurate sleep tracking as they can accurately determine your sleep stages, ie whether you’re in light, deep, or rapid eye movement (REM) sleep.
Dedicated sleep trackers
Apart from apps and wearables, an increasing number of devices are coming on to the market whose sole purpose is to monitor and track your sleep quality. These devices vary considerably in form and function, but their common feature is that they are designed to be used only in the bedroom.
Most dedicated sleep trackers work by placing sensors in the bed. These include the Beddit Smart, a wafer-thin adhesive strip which attaches to your mattress. Using a technology called ballistocardiography (BCG), Beddit ‘listens’ to your heart-rate and breathing patterns and converts these measurements into detailed metrics which you can analyse with the companion phone app. Beddit also detects body movement and snoring. A similar device, the Sleepace Reston, also features a thin sensor strip that you place under the sheets
By contrast, the ResMed S+ is a completely contact-free sleep tracking solution. It uses low-energy radio waves, like a bat’s-sonar, to pick up on your body movement and breathing patterns as you sleep.
Another interesting device is the Withings Aura. This ‘smart’ alarm clock features advanced light and sound sleep/wake programs, and coupled with the optional mattress sensor pad, the Aura delivers advanced sleep tracking functionality too.
Finally Eight, formally known as Luna, is a mattress cover with built-in sensors that can monitor your sleep habits at night, as well as integrating with smart-home devices like the Nest thermostat.
These are just a few of the popular bedroom-based sleep tracking solutions currently available. Although they perform less functions that multi--purpose activity trackers, in general, these dedicated sleep monitors offer more accurate sleep data than wearables and smartphone apps.
The future looks bright for sleep tracking. As more people become aware of the health implications of getting a good night’s sleep we will no doubt see more fascinating innovations in this new area of consumer health technology.
Jeff Mann is a sleep junkie, writer, entrepreneur and coffee shop philosopher. His latest project is sleeptrackers.io , bringing you the latest innovations in the world of wearable and in-bed sleep monitors.