Sleep trackers reviewed: Oura, Withings and Garmin Forerunner 945

June 20, 2020

Oura_ring

As we proceed further into the 21st century there is an increasing amount of sleep trackers we can use to monitor the quality of our sleep, all of them offering different type of data and feedback so we can quantify and cross-check our good nights rest. For the purpose of this review we will analyze 3 different types of sleep trackers:

  1. A smart ring (Oura)

  2. A sleep tracking mat (Withings)

  3. A sports watch (Garmin Forerunner 945)

Each of them will be reviewed based on their specificity and purpose and at the end a comparison will be provided to validate the results, tracking a total 3 days of sleep. If you are curious for the takeaway points scroll to the end.

1. Oura smart ring

Oura_Ring

The oura ring is the pet-peeve and a long time favorite of many health freaks and early adaptors. The ring is easy to wear and the team in Finland have improved the latest version so that it is a bit slimmer, with additional bonus points for style if you are flashing the stealth version.

Although it tracks activity during the day, there is not a whole lot of purpose of wearing the ring during the day aside from a special 'moments' functionality for meditation, it does not track a lot of metrics during the day.

During the night however, it reports sleep contributors and a total sleep score based on:

  • Total sleep
  • Efficiency
  • Restfulness
  • REM sleep
  • Deep sleep
  • Latency
  • Timing


What is really good about the Oura ring is it translates the various metrics into a readiness score which is based on even more data:

  • Resting heart rate
  • HRV balance (Heart Rate Variability)
  • Body temperature
  • Recovery index
  • Previous night
  • Sleep balance
  • Previous day activity
  • Activity balance

We see that the activity levels during the day may influence your readiness score. However, it has no influence on your sleep score. The readiness score is a great indicator for athletes to indicate how well they are rested for the day at hand. There are now also studies ongoing to use Oura as an early detection system for any type or illness or even COVID sypmtoms.

Probably the most valuable option is the Heart Rate Variability, and whilst there are a lot of inter-individual differences,  it is one of the best indicators for autonomic function and a stress-free state of mind. 

2. Withings sleep tracking mat

Withings_Sleep_Mat_1Withings_Sleep_Mat_2Withings_Sleep_Mat_3

Withings comes with an accompanying app called 'Health Mate'. The device can sync through the Wi-Fi connection and will automatically transfer the data to the app.The app contains a dashboard which covers three relevant variables:

  • Sleep
  • Sleep Apnea
  • Heart rate average

Key additions of the Withings sleep tracker mat is that it includes snoring detection, a sleep apnea score as well as heart rate monitoring. It does so by taking stock of any subtle movements that you make during the night. The mat can easily be placed below the mattress in order to start tracking sleep right away.

The post-sleep analysis provides the following insights:

  • Duration
  • Depth
  • Regularity
  • Interruptions
  • Time to sleep
  • Time to get up

Withings also offers the opportunity to manually record other things such as activities, blood pressure and food intake. And although the food tracker can be connected to the MyFitnessPal app, the activities do not seem to be integrated with any of the other available apps out there that do not require you to manually track activities.

3. Garmin Forerunner 945

Garmin_Forerunner_945

Let's be honest. This watch was not designed with the initial intent of providing world class sleeping support, but it was too tempting not to test when two other high quality tools were being measured. If you are a triathlete or any other multi-sport athlete, chances are you might be interested in this watch. The watch offers great extra functionalities like Garmin Pay, and tracks tonnes of metrics, but how many birds can you kill with one stone? 

The sleep tracker is not what they advertise this watch for, but can be found in the health trackers. There are 3 areas that can be tracked with the watch:

  • Sleep phases
  • Pulse oximeter
  • Breath frequency

The pulse oximeter is definitely a cool feature that this watch adds. And although it is not automatically installed, you can add it as an extra app and track it day and night. It is perhaps not 'medical grade' accurate, thus it is better to be used as a trend and not as an absolute. It is said that pulse oximetry can be used as a key identifier for sleep apnea as well. The oxygenated blood should in general be higher than 95%.

Garmin_Pulse_Oximeter_2Garmin_Pulse_Oximeter_1

Comparison of the 3 devices

1. Napping
Withings captures napping time on the sleeping mat, where both the oura ring and the Garmin 945 at the time of writing do not capture any napping time. This can be an important matter especially for any regular nappers or shift workers who work irregular hours and may therefore also sleep irregular hours.

2. Wearables
Another big upside of Withings, is in its ability not to wear anything bulky at night. Although some people like to display their fancy rings or watches, there is definitely something to be said as minimizing any wearables for comfort during the night.

3. Taking notes and journaling
Both Withings and Oura offer the opportunity to take notes in the app and to make any comments which can be valuable over time, when you want to identify any changes you have made in your habits which may affect your sleep either positively or negatively.

4. Respiratory rate
Respiratory rate is only tracked by Oura and Garmin. The Oura ring tracks this through 'photoplethysmography (PPG)'. It can be simply calculated based on your heart rate and your heart rate variability, which is tracked through the same method.

The Garmin seems to do the same thing but does a poor job properly explaining the proper mechanics behind it, in fact they redirect to it's firstbeat system, which explains a chest monitor would lead to more accurate results. 

People on the web tend to find that Garmin results for respiration rate tend to underrepresent the actual number of breaths per minute. When we compare it with Oura ring we come to the same conclusion, where the trend of Oura seems more reliable, stable and thus accurate.

Garmin_respiratory_rate_1Garmin_respiratory_rate_2Garmin_respiratory_rate_3Garmin_respiratory_rate_4Oura_respiratory_rate

Sleep accuracy

For the measurement of the accuracy of sleep, 3 consecutive days were tracked and the results will be presented.

DAY 1

Oura results

Oura_ring_1Oura_Ring_2

Withings results

Withings_1 Withings_2  Withings_4

Garmin results
Garmin_1

Overall results

1.Sleep score
Oura: 77 points
Withings: 88 points (bad depth)
Garmin: N/A

2. Total hours of sleep
Oura: 8h17m
Withings: 8h55m
Garmin: 9h23m

3. Total time in deep sleep
Oura: 1h14m
Withings: 41m
Garmin: 51m

4. Total time in REM sleep
Oura: 1h22m
Withings: 1h46m
Garmin: 2h51m

5. Latency:
Oura: 10m
Withings: 18m
Garmin: 2m

6. Avg. heartrate
Oura: 51 bpm
Withings: 51 bpm
Garmin: N/A in sleep score

DAY 2

1.Sleep score
Oura: 73 points
Withings: 85 points (good depth)
Garmin: N/A

2. Total hours of sleep
Oura: 7h18m
Withings: 7h52m
Garmin: 8h42m

3. Total time in deep sleep
Oura: 1h16m
Withings: 1h32m
Garmin: 59m

4. Total time in REM sleep
Oura: 1h31m
Withings: 2h39m
Garmin: 2h39m

5. Latency:
Oura: 13m
Withings: 30m
Garmin: 1m

6. Avg. heartrate
Oura: 49 bpm
Withings: 49 bpm
Garmin: N/A in sleep score

DAY 3

1.Sleep score
Oura: 81 points
Withings: 97 points (average depth)
Garmin: N/A

2. Total hours of sleep
Oura: 8h55m
Withings: 9h11m
Garmin: 9h28m

3. Total time in deep sleep
Oura: 1h32m
Withings: 1h33m
Garmin: 58m

4. Total time in REM sleep
Oura: 1h53m
Withings: 2h32m
Garmin: 2h58m

5. Latency:
Oura: 6m
Withings: 16m
Garmin: 0m

6. Avg. heartrate
Oura: 49 bpm
Withings: 49 bpm
Garmin: N/A in sleep score

Take away points

Based on the 3-day comparison and the multiple devices we have used, we can extract some anecdotal conclusions, for which of course the evidence can not be guaranteed.

  • Withings total sleep points are less accurate because of less amount of variables and lack of historical data taken into account.
  • Both Withings and Garmin overreport significantly on total amount of sleep. (note that sometimes I stay in bed to journal, Oura seems to account for that!)
  • Oura seems to be most accurate and consistent when it comes to deep sleep.
  • Oura seems to underreport however on REM sleep. Where both Withings and Garmin constistently report similar high numbers, and Oura varies.
  • I have the idea the latency of Withings is most accurate, as sometimes I have my doubts about the early sleep onset reported by Oura. Clearly the Garmin is not reliable there.
  • Average heartrate for both Oura and Withings over a full night are completely accurate.

Based on these points it seems that Oura ring still stands out in terms of accuracy, which should come as no surprise. With facebook groups with tens of thousands of members, I am convinced that the level of feedback for the ring, and surely the development team has had plenty of time for further optimization. 

However, if you are specifically looking for a non-wearable device that can track snoring or apnea as well, Withings definitely seems to be valid option. In fact the mat is tracking data more accurately than I expected. It is obvious that the Garmin Forerunner 945 should not be bought if your primary purpose is to use it as a sleep tracking device.

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