Eversleep 2 - by 

Darius Zoroufy, M.D. 



I tested the EverSleep 2 sleep tracking and management system.   

Over the last few years patients are asking more and more about the data their wearable devices tell them about their sleep.  The majority of these devices rely on an accelerometer to detect movement.  To understand how a fitness tracker can detect sleep, first we need to understand how it detects activity like counting your steps each day.  Fitness trackers use a very small system of capacitors to detect acceleration. Remember that acceleration is not velocity or speed.  That’s why your FitBit will not count any movement as you sit in seat 26E (middle seat) even though you are flying at 583 mph in a 737.    

In case your physics is a bit rusty, remember that acceleration is the change in velocity occurring in a specific time.  a = Δv / Δt  So when your wrist changes speed during your stride, the acceleration is detected and from that wrist movement, body movement is extrapolated.  Of course, your wrist may undergo acceleration and the accelerometer signals may be decoded incorrectly.  For example, I drove for 2 hours on a very bumpy road a couple of years ago. As my car bounced along, so did my wrist.  At the end of the drive my Fitbit had counted almost 4000 steps, even though I had only been sitting.   

(Here is a great demonstration of activity detected by a wrist accelerometer.)   

(If you really want to know how accelerometers work, check this out.

Even though fitness and activity trackers are not perfectly accurate, they can provide helpful information to guide our behaviors.  For example, my outdoor thermometer may be 3 or 4 degrees off, but it is accurate enough to let me know if I should wear a jacket.   

By 2016 more than 100 million fitness and activity trackers were made per year, and the market continues to grow.  The devices are getting better and adding more functions to distinguish themselves.   

Sleep occurs when cortex of the brain changes state and the electrical activity of the cortical cells begins to slow.  Sleep stages are measured by using an electroencephalogram in a controlled environment by a trained EEG or sleep technologist.  Electrodes are attached to the scalp to measure microvolt signals.  These recordings are interpreted using specialized equipment that costs hundreds of thousands of dollars.  Interpreting the data correctly requires years of training and experience 

Fitness and activity trackers shortcut this process by measuring sleep using the same accelerometer to estimate how deeply asleep you are.  These devices use record movements in a manner similar to a validated clinical sleep testing process called actigraphy.  Estimating sleep by recording wrist movement might seem wildly inaccurate, until you think about how your hands move while you are awake.  Beginning in infancy humans move their hands continuously as the output of their cognition and as their means for interacting with the world.  As we become drowsy and fall asleep, our sensory processing and cognitive activity decrease and consequently so do our hand movements.  The recorded wrist movements from an activity tracker can be interpreted to estimate sleep stages.  Fitness trackers that also measure heart rate can include that data to improve the accuracy of sleep stage determination.   

Recently, I bought an EverSleep 2 device, because it had features, I have not seen in other wearable devices.  EverSleep 2 was successfully crowdsource funded by IndieGoGo in 2017, receiving 224% of their target funding.  Since then EverSleep has become increasingly popular due to its many features that record physiological data and then present it in an organized, user-friendly app that provides interpretations of the data that are meaningful.  The app has additional features not seen in many other trackers:  it provides personalized sleep advice to modify behaviors to improve sleep quality.   

EverSleep 2 presents data in the app in an easily understood "Overview” display that give the user data about their sleep plotted on a graph that shows their specific numbers in relation to normal values.   


Under the “Details” tab the EverSleep app graphs the oxygen saturation, heart rate, motion, and sleep.  You can expand the graph to get a closer look at specific parts of the night.  They have even added a feature that is very helpful to sleep specialists:  the numerical and graphical data can be exported as a PDF to review with your physician.  The format of the PDF report is similar to the reports generated by clinical oximetry recording devices, so a physician will find it easy to integrate the data into a clinical assessment.   

Perhaps the most useful aspect of EverSleep 2 is the “Coaching” tab.  This feature takes the data from the nightly recordings and provides comments that reinforce positive data such as  

“Your profile says that you sometimes wake up during the night, but not last night!” 

“Sweet! CPAP seems to be working for you!” 

Each message has the option to “Read More” for more detailed information.   

The Coaching tab also provides specific comments that integrate the recorded data with the user-supplied data to provide personalized advice.   



Recording oxygen data is unusual for a consumer sleep tracker, but it is a very helpful feature.  EverSleep is careful to note that this is not a medical device, so it has not been validated to diagnose disorders or to direct treatment.  Nevertheless, the oximetry data can draw attention to potential areas of concern.  For example, if EverSleep detects episodes of low oxygen, it could suggest that sleep apnea or other respiratory disorders could be contributing to poor sleep.  If the person is already using CPAP or some other treatment for sleep apnea, EverSleep can confirm how well sleep apnea is controlled.   

Eversleep also records and detects snoring which could be a sign of sleep apnea, which can interfere with sleep quality and can increase the risk of cardiovascular disease.  In many cases, a person has no idea that they have sleep apnea.  Although EverSleep does not diagnose sleep apnea, it can detect snoring and oxygen changes that may suggest that further testing for sleep apnea is warranted.   

EverSleep 2 is extremely lightweight;  I barely felt that I was wearing it.  Since it is not an exercise tracker, it does not have to be rugged and waterproof.  The tracker itself is shaped like a watch with a thin band that hold it on the wrist.  The oxygen sensor probe extends from the tracker and wraps around a finger.  EverSleep suggests the user secure the sensor with a small piece of tape.  Once the tracker and sensor are in place and the app has been started it is easy to forget that it is there.  In the morning, simply remove the tracker and stop the recording.   

EverSleep 2 is currently for sale for $199, which purchases the sleep tracker that records sleep quality and sleep interruptions, sleep duration, movement, and snoring, as well as the oximeter which records oxygen levels and heart rate.  It also includes the app which interprets the data and provides meaningful, personalized assessments and recommendations.  I believe that EverSleep 2 will be a valuable tool to help many people improve their sleep quality and their health.   

 Check out EverSleep on Twitter: @GetEverSleep