A Guide To Tracking Your Sleep

"Quantimetric Self-Sensing" apparatus, 1996

“Quantimetric Self-Sensing” apparatus, 1996

Have you ever been curious about your personal sleep habits? Ever wondered whether you’re getting your full quota of rest every night?

Well now there’s no need to be kept in the dark – personal sleep tracking has hit the mainstream. And although the technology is still in its early days, it looks like it’s here to stay.

So, we’ve put together a definitive guide for anyone who wants to find out about personal sleep tracking technology. We hope you enjoy.

The quantified self

The last few years has seen an explosion of interest in gadgets and software designed to measure and evaluate our sleeping habits. Many factors have contributed to this – a growing awareness of sleep as a health concern, the ubiquity of smartphones, the rise in ‘big data’ analytics, a trend towards personalised healthcare – plus, of course, our inherent curiosity about ourselves.

The rise in sleep tracking stems from the phenomenon known as the ‘quantified self’ – a term used to describe those who use technology to collect data about themselves for personal development and to increase self-knowledge.

‘Self-tracking’ technology used to be expensive, bulky and complicated to set up. But Moore’s Law and the mass adoption of smartphones has changed all that. Nowadays millions of people are using gadgets to monitor aspects of their daily lives, including exercise, diet, heart-rate, location, alertness, mood, productivity and of course, sleep.

Why quantify?

The quest for self-knowledge is not exactly a new trend.Two thousand years years ago the maxim ‘Know Thyself‘ was carved into the Temple of Apollo in  ancient Greece. A few years ago the same sage advice made its way into the first Matrix movie. The 21st century, however has a new spin on self-knowledge. Instead of relying on contemplation or intuition, ‘quantified-selfers’ have access to cold hard data.

Gathering and analysing this data, over time, gives individuals great insight into whatever aspect of their lives they want to improve. Whether it’s getting fit, losing weight, getting smarter, or even curing disease, there’s most likely an app or a gadget out there to help you.

Why track sleep?

A recent report by the CDC called America’s sleep problems a public health epidemic. The report highlighted a growing concern over sleep-related issues such as:  the billions lost in economic productivity, fatal accidents caused by sleep deprivation, possible links with the obesity crisis, the rise in sleep apnea.

Despite the sum of human knowledge, sleep largely remains a mystery. Increasingly however, science is starting to build a case that sleep, along with proper nutrition and exercise is one of the three pillars of health.

Eating healthily and staying fit involve making conscious decisions. We can choose between having a salad or a burger, or taking the stairs instead of the escalator. But how do we know if the quality of our sleep is having an effect on our health?

Thankfully, sleep tracking technology can yield a lot of answers to questions such as: How many hours do I sleep each night? How long does it take for me to fall asleep? Do I sleep peacefully or am I a restless sleeper? Am I getting enough deep sleep, light sleep or REM? In addition

This information is compelling on its own, but if you’re serious about improving your health and well-being it can be invaluable when acted upon.

Sleep tracking – how the professionals do it


Polysomnogram patient

So, we’ve determined sleep tracking can be a force for good, but before you rush out and buy the latest gadget, it’s useful to take some perspective. Home sleep monitoring solutions, at least for the foreseeable future, will never give the same level of accuracy and diagnostic detail that a specialist sleep centre will provide.

The reason is simple. Consumer sleep tracking products are designed for a mass audience, often with value and simplicity a key part of the design ethos. A sleep centre clinician on the other hand is concerned with getting the most accurate medical diagnosis from his equipment.

Laboratory based clinical sleep tracking is known as polysomnography. Typically a polysomnogram (PSG) will involve connecting a spaghetti-like mass of wires, tubes and electrodes to various parts of your body. A single-night PSG can yield a lot of detailed information about your sleep; it’s also how doctors can tell if you’re suffering from sleep apnea.

Poly, meaning many, is a reference to the multiple types of test that run simultaneously while you are asleep. These include:

Brainwaves – an electroencephalogram (EEG): multiple electrodes attached to the scalp pickup your brain activity, which determines your sleep stages

Eye movement – electrooculogram (EOG): electrodes attached above and below the eye detect when your eyes are moving, giving an accurate indication of when you are in REM (rapid eye movement) sleep

Heart rateelectrocardiogram (ECG): electrodes attached to the chest  measure the electrical activity of the heart as it contracts and expands

Muscle tension – electromyogram (EMG): electrodes attached to the face and legs detect when your muscles relax and contract

Oxygen levels – pulse oximetery is a non-invasive way to measure oxygen levels in the blood

Breathing/air flow – sensors attached below the nostrils can detect any breathing abnormalities

Microphone – to record frequency and volume of snoring activity

One criticism of polysomnography is that the process itself can interfere with normal sleep. Spending a night in a hospital like environment, hooked up to dozens of wires is not most peoples’ idea of a restful sleep environment.

However it’s important to recognise that for now at least,  it’s not possible to produce the same level of diagnostic testing with consumer focussed technology. Home based sleep tracking may have the advantage of low cost and convenience it’s not a substitute for medical advice.

How accurate are personal sleep trackers?

We’ve already established that personal sleep tracking pales in comparison to a PSG in a sleep lab. But exactly how well do they compare? It’s a difficult question. The consumer electronics industry moves very fast. Peer-reviewed science on the other hand takes a long time. A 2012 study comparing a Fitbit activity, standard actigraphy, and PSG found the movement trackers had a tendency to “consistently misidentify wake as sleep and thus overestimate both sleep time and quality.”

However, such scientific papers become out of date as soon as a new gadget is released on the market.

Perhaps a more useful comparison is sleep specialist Dr Christopher Winter’s piece in the Huffington Post in Feb 2014. He took upon himself the task of evaluating 5 different sleep trackers, worn simultaneously whilst undergoing PSG in a sleep lab. In his test, the Basis tracker was the most accurate, with Jawbone and Fitbit devices performing less well. 24/7, a sleep tracking app for the iPhone came out worst in the test. You can view the results in the graph below.
Sleep trackers compared with polysomnogram (PSG)

How does sleep tracking work?

Advances in microelectronics and software designed have spawned a plethora of sleep tracking gadgets. Sophisticated components are now commonplace in phones, and can be tailored to monitor a range of inputs such as physical activity, direction, location, sound, skin conductivity, heart rate. Here are some of the key concepts  you need to be familiar with to get an understand how modern sleep tracking technology works:

Actigraphy – sensing your movment

Actigraphy is a non-evasive way of monitoring human rest/activity cycles. It is by far the most common method used for personal sleep tracking devices. In practice this usually consists of a wrist-worn device which measures and records bodily motion.

In contrast to a PSG, actigraphy seeks only to measure a single metric, movement. However because it’s cheap to deploy and can be used in the comfort of your own home it has been a popular tool for researchers for many years.

A 2011 study on wrist actigraphy usage in clinical settings concluded that ” Although actigraphy should not be viewed as a substitute for clinical interviews, sleep diaries, or overnight polysomnography when indicated, it can provide useful information about sleep in the natural sleep environment


accelerometer photo

Accelerometer chip

At the heart of every actigraphy device is something called an accelerometer. Using MEMS technology, these tiny components act as sensors, converting movement into electrical signals.

Once prohibitively expensive, accelerometer chips can now be manufactured for cents. Hence accelerometers can be found everywhere today; in your Iphone, your washing machines, and even shoes.

Beyond accelerometry

Whilst accelerometer devices are cheap and easy to manufacture, movement is not the most ideal or accurate way to measure sleep behaviour. Hence newer sleep tracking devices are starting to incorporate other ways to measure your vital signs whilst you’re asleep.

Heart rate

The advantage of measuring heart rate for sleep tracking purposes is that you can infer information about the sleep stages, (ie deep sleep, light sleep and REM). Although sleep staging can only reliably be measured with an EEG, as Dr Michael Breuss, the ‘Sleep Doctor‘ explains, “since each sleep stage has a signature heart rate, while not [a] direct measurement of sleep cycle, I think that this is certainly something that will be much closer than accelerometry”

There are many different methods for measuring heart rate, each with their pros and cons.

  • optical sensors (Basis, Pulse) measure your blood flow with light
  • bioimpedance sensors (Jawbone) measure electrical activity via the skin
  • ballistocardiography (Beddit, Misfit) measures the forces associated with heart contraction
  • non-contact sensors (Resmed, Nintendo) use radio waves to detect breathing, movement and heart rate

Brain waves

In some ways, personal sleep tracking has taken a step backwards. Up until a couple of years ago, the best sleep tracker was the Zeo Sleep Manager, a consumer EEG device whose accuracy was backed up by peer-reviewed studies. Sadly, Zeo ceased trading in 2013, a victim of competition from general purpose devices like the Fibit.

Zeo’s accuracy stemmed from its sensors were located on a headband, which amongst other things could take EEG readings, ie measure your brainwaves. None of the current crop of consumer sleep tracking devices offer this functionality, however Neuroon, a Kickstarter funded project promises to deliver ‘next generation technologies for sleep monitoring‘ with an eyemask that features EEG, EMG and EOG sensors.

Other options for EEG based sleep tracking are limited. One of the most interesting propositions, the award winning iBrain device from Neurovigil uses proprietary algorithms to give accurate EEG data using a single channel. However, the iBrain is only currently being used for research and there’s no plans for a consumer version.

Internet of Things (IoT)

The internet of things (IoT) is a concept of a world where everyday physical objects are equipped with network connectivity, allowing communication over the internet.

IoT has been happening for decades but smart, cheap sensor technology is now enabling it to become mainstream. From setting your thermostat, to monitoring global pollution, the internet of things will impact all of our lives.

Fitness and sleep tracking is another application of the IoT. Many devices already let you upload your sleep statistics to the internet for analysis. In the future, it’s likely we will see even more integration and connectivity between personal tracking hardware and ‘cloud’ software.

For example, both Jawbone and Fitbit, two of the market leaders in fitness tracking, have a software-platform which allows 3rd-party hardware to integrate with its software.  Similarly, Apple’s Healthkit and Google Fit platforms enable manufacturers and developers to access their services, allowing you to store all your health, fitness and sleep data in one place.

There’s no doubt we’re about to witness an explosion in interconnected devices and apps geared towards health, fitness and sleep. Whether we like it or not, the Internet of Things is here!

Types of sleep trackers

Sleep tracking apps

The simplest and most cost effective way to get started is by downloading an app for your iPhone or Android smartphone. Prices range from free to just a few dollars.

The beauty of using an app for sleep tracking is that you don’t have to buy any specialized hardware. The app uses your phone’s built-in accelerometer to measure your movement in bed at night.

There are literally hundreds of sleep-related apps available for Apple and Android devices. Four of the most popular at the moment  are Sleep GeniusSleepCycleSleepBot and Sleep Time.

The general principle for using standalone sleep tracking apps is simple. Before you hit the sack, make sure the app is turned on (and ideally plugged into the charger in case the battery dies) and simply place your phone under the pillow or somewhere on your mattress. The phone will do all the rest, tracking your body movements as you sleep.

Various apps differentiate themselves with add-on features, such as ‘smart’ alarm clocks – promising only to wake you when you’re in a light sleep-, white noise sounds to sooth you whilst asleep, and audio analysis to monitor noise disturbances or snoring.


But standalone apps have drawbacks. Accuracy is the main issue. For instance a memory foam mattress will respond differently  to one with soft springs, hence calibration is problematic. In addition phones have no way of distinguishing your movements from your bed partner, which can result in unreliable data.

Standalone sleep tracking apps may lack sophisticated hardware to give you a detailed analysis of your sleep patterns, but they’re the most cost effective way to start to gain some insight into your sleep habits.

Wearables and fitness trackers

The next step up from using a phone for sleep tracking is a wearable activity tracker. ‘Wearables’ usually combine sleep tracking capabilities with other functions including as fitness monitoring, calorie intake and heart-rate monitoring.

According to industry analysts, the world is about to go crazy for wearable technology. In 2014 tech giants Apple, Google, Microsoft and Intel all poured lots of money into wearable devices, whilst Morgan Stanley predicted that the business could be worth a staggering $1.6 trillion in the near future.

It’s easy to see why. The applications for wearables are incredibly diverse including communications, healthcare, fitness and wellbeing, home automation and even mobile payments. But there’s a problem at the moment. Over 50% of people who buy a fitness tracker or similar device, eventually lose complete interest

Why such a high drop-off rate? Users cite many problems; short battery life, poor design, tricky software, but essentially the technology is not yet mature enough to warrant mass adoption. Maybe this will change in 2015. Certainly there are no shortage of products to choose from. Although there are some exceptions, most wearable technology at the moment come in the form of wrist-worn actigraphy devices.

There are literally hundreds of different models on the market and many more in development. But this competitive market is currently dominated by a handful of companies who are leading the way in wearable fitness and sleep tracking. Here’s a brief rundown:

Jawbone: Previously known for its range of audio products , Jawbone launched the UP, a wrist worn activity tracking device in 2011. Its latest iteration, the UP3 bills itself as “the world’s most advanced tracker.” With sleek aesthetics and a 7-day battery life, the UP3 also features  a bio-impedance heart rate sensor to track your ‘true sleep stages’ .

BasisBasis markets it’s Peak the ‘ultimate fitness and sleep tracker‘. Its ‘Advanced Sleep Analysis’ captures multiple aspects of your sleep including: REM, deep and light sleep, toss-and-turn/ interruptions and sleep duration. The Peak falls into the smart-watch category, hence battery life is around 4 days.

FitBitFounded in 2007, Fitbit was one of the first companies to take fitness tracking to the mainstream. It’s latest product the Fitbit Surge features an optical heart rate monitor. Fitbit does not yet offer sleep stage analysis with its software.


The Withings Activite: a smart watch in disguise

Withings Activite


The long awaited announcement of Apple’s ‘iWatch’  in 2014 has led to renewed interest in multi-purpose wrist-worn gadgets. But are smart watches suitable for sleep tracking? The main problem for a watch-based sleep tracking solution is the short battery life. Aesthetics are important too. Not everyone wants to sport a ‘techie’  looking device on their wrist.

There are alternative’s however. The Activité by Withings, a Swiss watch maker, looks just like an ordinary analogue watch, but features activity and sleep tracking plus a whopping 2 year battery life compared to the meagre 24 hours Apple’s watch will give you.

Bed-based sleep tracking options

beddit_store_assets_2_black_1024x1024If you don’t want to wear a wristband in bed or you’re not interested in gathering fitness tracking data, you might want to consider one of the in-bed options for sleep monitoring.

Beddit, a Finnish company has created a thin-film sensor device which attaches to your mattress. Using ballistocardiography, the sensor claims to accurately measure heart-rate, respiration and movement and the makers provide links to scientific studies based on the device. Beddit recently teamed with another startup, Misfit to partner their respective software and hardware.

The Withings Aura is a contact free system to monitor and improve sleep. It consists of a sensor which you place under your mattress, and an ‘active light & sound ‘ bedside device. The device has less scientific credentials than the Beddit, but to make up for it you get a range of features including wake/sleep lighting effects, soft music and the ubiquitous ‘smart’ alarm clock

If you have deep pockets and luxury is your main concern, you might consider the X12 made by Sleep Number, an American company who make hi-tech adjustable beds. Costing a cool $8000 for the basic model, the X12 features SleepIQ technology, which can monitor and detect body movement, heart rate and breathing. Their technology  can also retrofitted to existing SleepNumber beds.

New innovations, different approaches

2014 was a very interesting year for new innovations in the sleep tracking market. As well as a whole host of wearable devices, a few other products stood out in terms of innovation and new approaches to monitoring your sleep.

Resmed S+

Resmed S+

Resmed was founded in 1989 to advance the treatment of sleep apnea and produced the first commercially available CPAP machine.  In 2014, it launched the Resmed S+, billed as world’s first non-contact sleep tracker. Using low-intensity radio waves to detect the subtle body movements, the S+ doesn’t required wristbands, mattress strips or electrodes.

In October 2014,the games company Nintendo, announced it is developing a sleep tracking device in partnership with Resmed. Given Nintendo’s mass market success in the gaming field, this looks like an interesting proposition to bring sleep tracking to a wider public

The Sense by startup Hello Inc, is a futuristic looking orb, which sits on your bedroom table and monitors aspects of your sleeping environment including light, motion, humidity, sound, and even the air quality. A non-contact solution, Sense uses actigraphy to track your sleep, with the aid of a small ‘pill’ with attaches to your pillow.

Sleep tracking and your data

One of the ironies about the quantified ‘self’ movement, is that by uploading your tracking data to any of the ‘cloud’ providers, you by default waves any rights to sole ownership of your personal data.

Aggregating ‘big data’ from users has become the de-facto business model for technology companies. Although you give it away for free, your personal data holds great value for the giant databases Apple, Google, et al – in terms of both commerce and research.

For example, Jawbone recently published a fascinating set of reports, based on tens of thousands of UP wristband users. Among the findings we learn that Toyko is the most sleepless city, averaging 5h 44min, and Swedish people are the biggest walkers.

This kind of data may seem innocent and benign on the surface, but the potential value is immeasurable to an array of interested parties, be they pharmaceutical companies, insurers, doctors or even employers.

So it’s important to ask yourself the question – do you feel 100% comfortable sharing your data online?


The future looks bright for sleep tracking. With tech giants Apple and Google pushing their health platforms, and a wearables industry about to explode, a lot of people over the next couple of years will be tempted to join the legions of quantified self’ers already out there.

But some doubts and questions remain about the long term viability of such technology. What happens once you’ve ‘diagnosed’ your sleep problems or made adjustments to your lifestyle to correct bad habits? Will people want to continue monitoring themselves for the sake of it or will your wristband be consigned to the bottom drawer after six months?

Whether or not sleep tracking becomes a fad or goes mainstream, it’s hard to feel negative towards a movement that is surely destined to raise awareness about the many life-enhancing ways that sleep can benefit our daily lives.

This article was originally published at Sleep Junkies

Photo Credits

Photo by SparkFunElectronics

QuantimetricSelfSensingPrototypeMann1996inset  via Wikimedia Commons

Photo by Todd Huffman

Photo by Jason A. Howie