WHOOP’s the Best, Ultrahuman Is the Easiest to Use

Sleep is one of the most important factors in your health and performance, yet most of us have no objective way of measuring it. That’s where sleep trackers come in.

Unfortunately, not all sleep trackers are created equal. Some devices offer highly accurate data with actionable insights, while others are little more than expensive gimmicks.

In this article, I’ll break down the best sleep trackers based on scientific research, validation studies, their underlying technology and my personal experience testing them.

At the end of the article, I’ve also listed two sleep trackers I don’t recommend (including one popular option from Fitbit) due to inaccurate data, a lack of reliability, or the absence of key features that are necessary for extracting useful data from the device.

Best Overall: WHOOP 4.0 Health and Recovery Tracker

In addition to being one of the most accurate fitness tracking devices on the market today, WHOOP is also the most advanced and most reliable wrist-worn sleep tracker, thanks to the inclusion of four different sensors that sample data 100 times per second. These sensors include:

• Optical heart rate sensor with pulse oximetry capability, which improves the capture of heart rate data during sleep.
• A 3D gyroscope to detect movement and respiratory rate. Both of these biometrics can be used to identify sleep stages. For example, you normally don’t move during deep sleep and your respiratory rate is lower than during REM or light sleep.
• Skin conductance to detect changes in electrodermal activity, which changes when you fall asleep or when you’re stressed.
• Ambient temperature monitor to detect changes in skin temperature. Your skin temperature drops when you fall asleep and changes throughout the night, based on your sleep cycle.

Combined with a machine learning algorithm that constantly learns from the anonymous data provided by other WHOOP users, these sensors make for an extremely powerful device that is able to provide you with accurate data and actionable insights for improving your sleep.

WHOOP also helps you correlate your lifestyle choices (such as alcohol consumption, meal timing and workout intensity) with changes to your sleep quality, features a sleep coach that recommends the ideal bed and wake time for optimal sleep performance based on your individual data and health metrics, and has a smart alarm that can wake you up silently using gentle vibrations.

You can learn more about these features and how they work in the sleep tracking section of my in-depth WHOOP review.

Try WHOOP

Use the link above to get a free month of WHOOP (no promo code required).

Most Convenient: Ultrahuman Ring Air

The Ultrahuman Ring Air has sensors for measuring heart rate, body temperature, respiratory rate, skin temperature, heart rate variability, blood oxygen saturation, movement and other biometrics several times per second.

Most wearable sleep trackers are designed to be worn on the wrist, which can be inconvenient if you’re someone who regularly wears a watch or wrist-worn jewelry. The Ultrahuman Ring Air is an appealing option for these use cases, thanks to its very small form factor.

One knock against Ultrahuman is a lack of validation from studies involving real-world data from a combination of regular users and elite athletes. As a result, it’s difficult to tell how accurate the device really is in comparison to polysomnography (PSG), which is considered the gold standard of sleep tracking.

However, the science team at Ultrahuman conducted a pilot study comparing the Ring Air with the Apple Watch and concluded that, “Performance of the Ultrahuman Ring Air is within the ranges of other wrist and finger-based sleep trackers.” 

It’s worth noting that the study only examined total sleep time, wake-ups and total time awake, ignoring the amount of time participants spent in the various stages of sleep, including deep and REM sleep.

To learn more about this sleep tracker and its capabilities, check out my in-depth comparison of the Ultrahuman Ring Air and the Oura Ring Gen 4.

Visit Ultrahuman

If you want to give the Ultrahuman ring a try, make sure to use discount code MIK to get 10% off the MSRP.

Most Accurate: Muse S Brain-Sensing Headband

Muse S is a brain-sensing headband that I’ve been using to get real-time feedback on my brain activity during meditation sessions. However, it’s also an incredibly accurate sleep tracker because it uses electroencephalography (EEG) technology — in combination with an optical heart rate sensor and a gyroscope — to monitor your brain waves in order to identify what stage of sleep you’re in.

Your brain waves change depending on sleep phase, so EEG is arguably the most accurate sleep tracking technology available to consumers.

In addition to reporting your total time asleep and the time you spend in the various stages of sleep, the Muse app records your sleep position and heart rate. All of this data is packaged up into a sleep quality score that gets reported every morning.

The biggest downside to Muse S is that it streams your sleep data to your phone via Bluetooth, instead of storing everything locally and then synchronizing it with the phone. This means you’re constantly exposed to Bluetooth radiation while sleeping.

Additionally, it’s worth noting that Muse S is not quite as comfortable as wrist-worn devices (or the Ultrahuman Ring Air). Don’t get me wrong: Muse S is as comfortable as a headband can be. But I generally prefer having a device strapped to my wrist rather than my head.

If you want to give Muse S a try, you can use the link below. Make sure you use code MKUMMER to get 10% off your purchase.

Visit Muse S

To learn more about Muse S and how I use it for both meditation and sleep tracking, check out my in-depth Muse S review.

Best Non-Wearable Option: Eight Sleep Pod 4 Bed Cooling System

The only non-wearable sleep tracking device that I’ve found to be relatively accurate and reliable is Eight Sleep’s Pod 4, which is a water-based, temperature-control smart mattress that has a series of built-in sensors called “the Active Grid.”

I’ve been using Eight Sleep to track my sleep for the past few years. Based on the comparison data I’ve collected, the Pod system’s tracking capability is more or less in-line with WHOOP and the Ultrahuman Ring Air.

More specifically, I’ve found that it’s incredibly accurate at measuring heart rate, heart rate variability, sleep onset and sleep disturbances (i.e., wake-ups). It’s also fairly accurate at measuring deep and REM sleep, though I’ve seen some variance in that data when compared to other devices.

Of course, the big advantage is that you don’t need to wear a tracker on your body. Additionally, Eight Sleep’s temperature control system gives you the tools to not only measure but actively improve your sleep.

You can learn more about the Pod system in my in-depth Eight Sleep review.

If you want to give it a try, you can use the link below and enter promo code KUMMER at checkout to get $100 to $200 off (depending on which model you purchase).

Visit Eight Sleep

Best Smartwatch for Sleep Tracking: Apple Watch Series 10

Considering that the Apple Watch’s heart rate sensor and ECG feature are both FDA-approved, and are incredibly accurate according to third-party testing, you would expect the device’s sleep tracking to be at least fairly accurate.

However, the sleep data reported by my Apple Watch Ultra (running watchOS 9 at the time) never matched the data reported by my other (more technologically-advanced) sleep trackers, including WHOOP 4.

For example, my Apple Health data over a 30-day period said that I spent an average of 0:39 in deep sleep and 1:34 in REM sleep. Those are very low numbers, and, just based on how I feel every morning (both physically and mentally), I think the Apple Watch underreports deep sleep.

I’m not sure if that’s because of the relatively slow HR sampling frequency (every few minutes), the lack of additional sensors, or something that I do (e.g., a lack of arm movement or my resting heart rate).

But I’m also aware of other users, such as this YouTube creator, who claim the Apple Watch has been reliable in tracking sleep and the various stages of sleep. So there is a chance that the Apple Watch works reliably for some but not all users.

If you’d like to learn more about the sleep tracking capabilities of the latest-generation Apple Watch, you can check out my in-depth WHOOP vs Apple Watch article, which goes into more detail about the device’s sensors, how it attempts to track sleep, and other important details.

Apple Watch Series 10 on Amazon

Sleep Trackers I Don’t Recommend

These devices might accurately track your heart rate, but I doubt — given their technological limitations — that they can reliably track your sleep (and your stages of sleep in particular).

The sleep trackers I don’t recommend include:

Fitbit Sense

Fitbit offers a range of smartwatches and fitness straps that the company claims can accurately track sleep. Their flagship model is the Fitbit Sense, which offers sleep tracking via a combination of an optical heart rate tracker, a MEMS three-axis accelerometer, and a skin conductance sensor.

Considering that the Fitbit Sense has all the necessary sensors to offer relatively accurate sleep tracking capabilities, I was disappointed to discover that it fails to effectively leverage that technology.

In my tests, neither the total time asleep nor the sleep stages data was accurate and comparable to WHOOP and Eight Sleep (as I discussed in my Fitbit vs. WHOOP comparison article).

I’ve even heard some reports of the Fitbit Versa incorrectly recording HR data while it wasn’t even being worn.

If the software algorithm in the Fitbit Sense can’t even tell the difference between a real pulse and light reflected by a countertop (which may have been the case in the example linked above), I have no trust in its ability to distinguish between the various stages of sleep.

Withings Sleep

Withings Sleep is an under-the-mattress device that can supposedly track your overall sleep, sleep stages, respiratory rate, heart rate and snoring.

The idea behind this product is that your beating heart, breathing or snoring all cause different movement patterns that the sensor can pick up.

As I mentioned before, I’m skeptical of whether a $129 device can accurately pick up and correctly identify those patterns, especially if several of them happen concurrently.

Final Thoughts: Are Sleep Trackers Accurate Enough to Be Worth It?

Accurately tracking sleep is difficult, because most of the consumer-grade devices we have access to can’t measure brain waves, which are the only direct indication of sleep.

Instead, wearable and contactless sleep monitors have to use proxies like movement, heart rate, skin conductance, ambient temperature and respiratory rate to make an educated guess as to whether a person is truly sleeping or not.

Besides getting quality data from as many different biometric sensors as possible, it’s up to the underlying software algorithm to make sense of the data and report back to the user.

The algorithm is where I think most sleep trackers fall short. It takes validation studies and large amounts of data for algorithms to reliably predict if a subject is sleeping and in what stage of sleep the person is in.

Based on everything I’ve seen, there are only a handful of sleep trackers out there that have both the underlying technology and algorithm to accurately track and help you improve your sleep.

All the other trackers are gimmicks that might over-report or under-report your sleep, and are thus virtually useless if your goal is to introduce meaningful lifestyle changes that result in better health and performance.

However, it’s vital to keep in mind that no consumer-grade sleep tracker is perfect. To accurately measure your sleep and how much time you spend in each of the stages of sleep you need a gold-standard sleep study conducted in a lab using polysomnography (PSG).

At the same time, the best sleep trackers can still provide valuable insights for optimizing your sleep habits.

Michael Kummer is a healthy living enthusiast and CrossFit athlete whose goal is to help people achieve optimal health by bridging the gap between ancestral living and the demands of modern society.