Apps and fitness trackers that measure sleep: Are they useful?

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Consumers have become increasingly interested in using fitness trackers and smartphone applications to quantify sleep. The devices claim to measure various sleep parameters, with the result that patients are now showing the data from their devices to their clinicians with concerns about their quantity or quality of sleep. In general, these devices have major shortcomings and limited utility, as they have not been thoroughly evaluated in clinical populations.


  • Wearable fitness trackers tend to perform better than smartphone applications, which are more prone to interference from bed partners and pets.
  • Sleep data from tracking devices are less reliable in patients with fragmented sleep and insomnia.
  • In normal sleepers, devices tend to measure sleep duration with reasonable accuracy, so that one can tell if a patient is getting too little sleep or reassure someone who is getting enough sleep.
  • Devices may help identify patients with poor sleep hygiene or atypical circadian rhythms.



More and more consumers are using wearable devices and smartphones to monitor and measure various body functions, including sleep. Many patients now present their providers with sleep data obtained from their phones and other devices. But can these devices provide valid, useful clinical information?

This article describes common sleep tracking devices available to consumers and the mechanisms the devices probably use to distinguish sleep from wakefulness (their algorithms are secret), the studies evaluating the validity of device manufacturers’ claims, and their clinical utility and limitations.


Close to 1 in 10 adults over age 18 owns an activity tracker, and sales are projected to reach $50 billion by 2018.1 Even more impressive, close to 69% of Americans own a smartphone,1 and more than half use it as an alarm clock.2

At the same time that these devices have become so popular, sleep medicine has come of age, and experts have been pushing to improve people’s sleep and increase awareness of sleep disorders.3,4 While the technology has significantly advanced, adoption of data from these devices for clinical evaluation has been limited. Studies examining the validity of these devices have only recently been conducted, and companies that make the devices have not been forthcoming with details of the specific algorithms they use to tell if the patient is asleep or awake or what stage of sleep the patient is in.


Consumer tracking devices that claim to measure sleep are easily available for purchase and include wearable fitness trackers such as Fitbit, Jawbone UP, and Nike+ Fuelband. Other sleep tracking devices are catalogued by Ko et al.5 Various smartphone applications (apps) are also available.

Fitness trackers, usually worn as a wrist band, are primarily designed to measure movement and activity, but manufacturers now claim the trackers can also measure sleep. Collected data are available for the user to review the following day. In most cases, these trackers display sleep and wake times; others also claim to record sound sleep, light sleep, and the number and duration of awakenings. Most fitness trackers have complementary apps available for download that graphically display the data on smartphones and interact with social media to allow users to post their sleep and activity data.

More than 500 sleep-related apps are available for download to smartphones in the iTunes app store5; the Sleep Cycle alarm clock app was among the top 5 sleep-tracking apps downloaded in 2014.6 Because sleep data collection relies on the smartphone being placed on the user’s mattress, movements of bed partners, pets, and bedding may interfere with results. In most cases, the apps display data in a format similar to that of fitness trackers. Some claim to determine the optimal sleep phase for the alarm to wake the user.


Older activity-tracking devices used single-channel electroencephalographic recordings or multiple physiologic channels such as galvanic skin response, skin temperature, and heat flux to measure activity to determine transitions between periods of sleep and wakefulness.7,8

None of the currently available consumer sleep tracking devices discloses the exact mechanisms used to measure sleep and wakefulness, but most appear to rely on 3-axis accelerometers,9 ie, microelectromechanical devices that measure front-to-back, side-to-side, and up-and-down motion and convert the data into an activity count. Activity counts are acquired over 30- or 60-second intervals and are entered into algorithms that determine if the pattern indicates that the patient is awake or asleep. This is the same method that actigraphy uses to evaluate sleep, but most actigraphs used in medicine disclose their mechanisms and provide clinicians with the option of using various validated algorithms to classify the activity counts into sleep or awake periods.9–11

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