Is the Galaxy Watch 8 Health Tracking Accurate?

TL;DR

Early testing suggests the Galaxy Watch 8 tracks heart rate well and may offer promising sleep-stage detection. Two indoor cycling sessions produced a heart-rate correlation of 0.96, while one usable sleep recording showed about 80% deep-sleep agreement and 75% light-sleep agreement against a Zmax EEG headband, although more nights and activities are needed before drawing firm conclusions.

Transcript

I've been using the Galaxy Watch 8 for a whole weekend now and I have some thoughts that I want to share with you in this video. Now, for those of you who don't know me, my name is Rob and I'm a post-doctoral scientist specializing in biological data analysis. So, today we're going to take a look at the bunch of data I gathered with the Galaxy Watc... Read More

Key Insights

• The Galaxy Watch 8 showed promising heart-rate performance across early exercise tests. The reviewer collected data during a 9K run, indoor and outdoor cycling, and weightlifting to determine whether improvements seen in an initial review were consistent rather than a chance result.
• Sleep-stage accuracy was evaluated against a Zmax EEG headband designed to measure brain waves for sleep-stage tracking. This reference allowed the reviewer to compare the watch's classifications of deep, light, and REM sleep with independently measured sleep-stage data.
• The usable sleep recording showed about 80% agreement for deep sleep and about 75% agreement for light sleep. REM sleep produced the weakest agreement, although the reviewer still judged its performance promising because many consumer devices struggle with that stage.
• Deep-sleep timing was almost perfectly aligned during the single analyzed night. The Galaxy Watch 8 also identified most apparent REM segments near the ends of sleep cycles, but it added REM early in the night and disagreed more near the final period of interrupted sleep.
• The sleep analysis was limited to one usable night because the Zmax reference disconnected during the other recording and created gaps in its data. The reviewer repeatedly cautioned that the apparent accuracy could change substantially after collecting and analyzing more nights.
• The Galaxy Watch 8 would fall near Fitbit, Pixel Watch, and Whoop devices if the single-night sleep result remained representative. In the reviewer's comparison, it did not appear as strong as the Apple Watch, Eight Sleep Pod, Oura Ring, or Sleep 2 app.
• Indoor cycling heart-rate tracking produced a correlation of 0.96 across two sessions. The reviewer described this performance as good enough, though not amazing, and noted slightly more total deviation than appeared in the earlier session reviewed before this weekend test.
• The review remained preliminary because some collected data had not yet been analyzed. The reviewer planned a later comprehensive assessment covering more Galaxy Watch 8 recordings, along with data from the Galaxy Watch Ultra and Galaxy Watch Classic after those devices became available.

Questions & Answers

Q: How accurate is Galaxy Watch 8 heart-rate tracking?

Early heart-rate results were encouraging across several exercise types, including a 9K run, cycling, and weightlifting. The clearest reported figure came from two indoor cycling sessions, which produced a correlation of 0.96 with the reference measurements. The reviewer considered that good enough but not amazing, noting some deviation and reserving a final judgment until additional data could be analyzed.

Q: How accurate is Galaxy Watch 8 sleep tracking?

The single usable night showed promising sleep-stage tracking against a Zmax EEG headband. About 80% of the periods labeled deep sleep by the reference were also classified as deep sleep by the watch, while light-sleep agreement was about 75%. REM agreement was the weakest of the three stages, but the reviewer still considered it relatively good for an early result.

Q: What device was used to test Galaxy Watch 8 sleep stages?

The Galaxy Watch 8 was compared with a Zmax EEG headband, a device designed for sleep-stage tracking that can measure brain waves. The reference classifications appeared along the top of the reviewer's analysis, while the watch classifications appeared on the left and in the lower portion of the nightly timeline. Computer code was then used to calculate and visualize agreement.

Q: Why was only one night of Galaxy Watch 8 sleep analyzed?

Two nights of sleep data were collected, but the Zmax reference device disconnected during one night and left visible gaps in its recording. That made the reference night unsuitable for the intended comparison. Consequently, the preliminary sleep conclusions relied on only one usable night, which the reviewer said should be treated with a very large grain of salt.

Q: How well did Galaxy Watch 8 detect deep and REM sleep?

Deep-sleep detection was the strongest part of the single-night analysis, with about 80% agreement and nearly perfect alignment in the plotted nightly timeline. REM detection was weaker but still captured most apparent REM segments near the ends of sleep cycles. The watch incorrectly added some REM early in the night and showed further disagreement near the interrupted end of sleep.

Q: How does Galaxy Watch 8 sleep tracking compare with other devices?

If the one-night result remained representative, the Galaxy Watch 8 would sit in the reviewer's second tier near Fitbit devices, the Pixel Watch, Fitbit Charge 6, and Whoop Strap. It appeared below the group containing Apple Watch, Eight Sleep Pod, Oura Ring, and the Sleep 2 app. The reviewer stressed that more nights were required before making a recommendation.

Q: What exercises were used to test Galaxy Watch 8 heart rate?

The weekend testing included a 9K run, cycling trips, indoor cycling, and a quick weightlifting session. These activities were chosen to add more heart-rate measurements and test whether the strong performance seen in the initial review continued across additional sessions. At the point covered by the transcript, detailed results were reported for two indoor cycling sessions.

Q: What additional Galaxy Watch 8 testing was planned?

The reviewer planned to analyze more heart-rate recordings, additional sleep nights, and GPS data from a run completed in repeated circles. The overlapping circular route was intended to reveal positional deviation in the GPS track. A later comprehensive review was also planned, including the Galaxy Watch 8, Galaxy Watch Ultra, and Galaxy Watch Classic after the other watches arrived.

Summary & Key Takeaways

• The reviewer, a postdoctoral scientist specializing in biological data analysis, tested the Galaxy Watch 8 over a weekend. He focused mainly on heart-rate and sleep-stage tracking, using exercise sessions for heart-rate data and a Zmax EEG headband as the sleep reference. GPS data from a circular running route was also collected for later inspection.

• Only one of two recorded nights provided usable reference data because the Zmax disconnected during the other night. In the usable comparison, the watch matched roughly 80% of reference deep sleep and about 75% of reference light sleep. REM agreement was weaker, but the overall pattern still appeared promising for this preliminary test.

• Heart-rate results remained encouraging after additional running, cycling, and weightlifting data were collected. Across two indoor cycling sessions, the Galaxy Watch 8 achieved a correlation of 0.96 with the reference measurements. The reviewer considered that result good enough, while emphasizing that a comprehensive assessment would require more nights, sessions, and completed analyses.