Measuring Rem Sleep: Can An App Really Work?

Sleep is a mysterious, multifaceted process that involves various stages, including REM sleep, which is characterised by rapid eye movement, brain activity, and dreaming. Understanding sleep patterns can provide valuable insights into overall health and well-being. As a result, many people are interested in tracking their sleep to optimise their sleep habits and enhance their sleep quality. This has led to the emergence of numerous sleep-tracking apps that claim to provide detailed information about sleep cycles and offer recommendations for improvement.

While these apps can be intriguing, the question arises: Can they really measure REM sleep accurately?

How do sleep apps work?

Sleep apps work by tracking your sleep patterns and habits to help you understand your sleep quality and duration. They use various methods to collect data, including sound detection, sonar, movement tracking, and optical heart-rate monitoring. This data is then analysed to provide insights into your sleep cycles and make suggestions for improvement. While they don't offer clinically accurate readings, they can help identify trends and patterns. Here's a more detailed look at how sleep apps work:

Data Collection

Sleep apps employ a range of methods to collect data about your sleep:

• Movement Tracking: Accelerometers interpret stillness as sleep and movement as wakefulness. However, this method has limitations as it may mistake lying still for sleep and count tossing and turning as being awake.
• Sound Detection: Phone apps analyse the sounds of various movements during sleep. Less movement is assumed to be deep sleep, while more movement indicates light sleep.
• Sonar: Phone speakers emit inaudible sound waves that bounce off your chest as you breathe, and the phone's microphone picks up these deflected waves for analysis.
• Optical Heart-Rate Monitoring: Devices like fitness trackers and smartwatches use LEDs to shine light through the skin and capture blood flow data. Changes in heart rate are correlated with different sleep stages.

Data Analysis and Insights

Sleep apps analyse the collected data to provide insights into your sleep:

• Sleep Duration: Apps can track the time you're inactive to estimate when you fall asleep and wake up.
• Sleep Quality: They can detect interrupted sleep by identifying periods of tossing and turning.
• Sleep Phases: Some apps attempt to track sleep phases and time alarms to go off during lighter sleep, making it easier to wake up.
• Environmental and Lifestyle Factors: Some apps record factors like light, temperature, caffeine intake, and stress levels to identify their impact on sleep.

Suggestions and Improvements

Based on the data analysis, sleep apps may offer suggestions to improve your sleep:

• Sleep Goals and Schedules: You can set sleep goals and create customised schedules to meet those goals.
• Sleep Hygiene: Apps may provide advice on pre-sleep routines, such as avoiding screens and late-night meals.
• Relaxation Techniques: Some apps offer meditations, sleep stories, and breathwork exercises to help you relax and fall asleep.
• Smart Alarms: These features wake you up during light sleep, making it easier to get up.

Limitations and Considerations

While sleep apps can be useful, it's important to consider their limitations:

• Accuracy: Sleep apps don't provide clinically accurate readings. They estimate sleep based on movement and heart rate, which are not definitive indicators of sleep stages.
• Comparison to Polysomnography: Polysomnography, used by experts, tracks brain waves, heart rate, breathing, blood oxygen, and body movements—providing a more accurate analysis.
• Insomnia and Mental Health: Sleep apps may underperform for people with insomnia and could potentially worsen mental health issues by causing sleep-related anxiety.
• Data Privacy: Always review an app's privacy policy before use, as your data may be shared with third parties.

Are sleep apps accurate?

Sleep-tracking apps are not 100% accurate, but they can be useful for helping you recognize patterns in your sleep habits. They can shine a light on your biggest source of inactivity: sleep.

Sleep trackers can monitor:

• Sleep duration
• Sleep quality
• Sleep phases
• Environmental factors
• Lifestyle factors

However, they don't measure sleep directly. Instead, they often measure inactivity as a surrogate for estimating sleep. Most sleep-tracking devices make some guesstimate as to how much you're actually sleeping.

For exact data about your sleep habits, you'd have to do a medical sleep study, which monitors brain waves to analyze the stages of sleep you cycle through during the night. Such studies are helpful for diagnosing conditions like sleep apnea and other sleep disorders.

If you're looking for a more accurate sleep-tracking solution, you might consider a dedicated sleep-tracking device. These usually take the form of a wearable device, such as a ring, a wristband, or a clip that attaches to your pillow. Some examples include:

• Oura Ring
• Fitbit
• Apple Watch
• Bose sleep-aid earbuds

While these devices may offer more accurate sleep tracking than apps, it's important to note that even they are not as reliable as a medical sleep study.

What are the best sleep apps?

Sleep apps can be a great way to help you fall asleep, stay asleep, and understand your sleep patterns. However, they are not a replacement for medical advice or a clinical sleep study. Here are some of the best sleep apps available:

• SleepScore: This app was recommended by reviewers at Wirecutter, who described it as the "most intuitive and convenient app" they tested. SleepScore allows you to set sleep goals and provides advice for reaching them. It also offers more detailed sleep-stage data than most other apps and has a smart alarm that wakes you up slowly. The free version provides general sleep advice and a record of your sleep for seven days. The premium version costs $50 a year or $6 per month and offers long-term sleep tracking and helps you create a path toward improvement. However, SleepScore only works with iPhone 6 and higher and a limited number of Android phones.
• Sleep Cycle: This app was recommended by both Wirecutter and Verywell Mind. It is compatible with both iPhones and Android phones and has a clean interface with easy-to-understand graphs. Sleep Cycle also has more than a dozen smart-alarm sounds and lulling sounds to choose from. However, it falls short in providing detailed sleep-stage data and giving advice for improving sleep.
• Calm: Recommended by Verywell Mind, Calm was chosen as the best app for falling asleep due to its extensive library of sleep sounds, meditations, and sleep stories. It features celebrity cameos, officially licensed titles, and various music playlists. Calm offers a free version with limited content and a premium version for $15 per month or $70 per year.
• Pillow: Pillow was recommended by both CNN Underscored and Verywell Mind. It offers audio recordings, sleep trends, heart rate and oxygen saturation tracking, sleep sounds, a nap mode, bedtime reminders, and personalized insights to improve your sleep. Pillow provides detailed reports each morning, including sleep quality score, sleep stage analysis, heart rate, and blood oxygen readings. The free version has limited content, while the premium version costs $10 per month or $40 per year.
• Oura: Oura was recommended by Verywell Mind as the best app for technology. It is a device you wear on your finger that measures heart rate, movement, and temperature to identify sleep stages. The app provides an easy-to-read chart of different sleep stages and an overall sleep and readiness score each morning. Oura also highlights patterns and changes in your sleep over time. The Oura ring costs $299, and the app has a monthly membership of $6 to access all data and insights.
• SleepWatch: SleepWatch was recommended by Verywell Mind as the best app for Apple Watch users. It seamlessly integrates with the Apple Watch and automatically collects data on sound, bedtime, heart rate, and movement to track your sleep cycles. SleepWatch provides a sleep score and an in-depth analysis of your sleep, including length of sleep and variations in heart rate. It also has a white noise composer that allows you to create a custom mix. The premium version costs $5 per month or $40 per year.
• ShutEye: ShutEye was recommended by CNN Underscored as an all-in-one option, offering a variety of sleep sounds, sleep stories, relaxing music, and a built-in sleep tracker that uses your phone's microphones to understand your sleep cycles.
• BetterSleep: BetterSleep was recommended by CNN Underscored for its scientific approach to sounds and music for relaxation and falling asleep. It uses different tones and keys optimized for specific use cases to help you relax and fall asleep. BetterSleep also includes a sleep tracker, sleep stories, and more. It costs $10 per month, $60 per year, or $250 one-time after a seven-day trial.

How much do sleep apps cost?

Sleep apps can be free or low-cost, with the paid options often providing a one-week free trial. Monthly fees generally range from $5 to $15. For example, SleepWatch costs $5 per month or $40 per year, while Calm costs $15 per month or $70 per year.

SleepScore is free to download, but the premium version costs $50 per year or $6 per month. Pillow is free, but Pillow Premium is $10 per month. Sleep Cycle costs $10 per month or $40 per year.

Some apps have more expensive options, such as Calm, which offers a $400 lifetime subscription, and Sleep Reset, which costs $300 for an eight-week plan after a pay-what-you-can seven-day trial.

The Oura Ring is a device that works with a sleep app and costs $299, with a $6 per month membership fee.

Do you need a wearable device to use a sleep app?

Sleep apps can be used with or without a wearable device. However, the accuracy of the data collected by the apps is increased when paired with a wearable device.

Sleep apps that don't require a wearable device rely on sound analysis or movement tracking to estimate sleep patterns. For example, Sleep Cycle uses sound analysis to identify sleep states and Sleep as Android uses movement tracking. However, these methods may not be as accurate as those used by wearable devices. For instance, Sleep Cycle may pick up on sounds from others in the room, and movement tracking may perceive someone as sleeping when they are just lying still.

Wearable devices, such as smartwatches and fitness trackers, often use optical heart-rate monitoring or accelerometers to track sleep. Optical heart-rate monitoring involves using tiny LEDs in the device's band to shine a light through the skin and capture blood flow. Accelerometers interpret stillness as sleep and movement as wakefulness. Wearable devices can also be used in conjunction with sleep apps to increase their accuracy. For example, Pillow works best when paired with an Apple Watch, and Sleep as Android supports a wide variety of smartwatches.

Frequently asked questions