Apple Watch Series 12 - Ultimate Scientific Review!
In a Nutshell
The Apple Watch Series 12 delivers excellent heart rate tracking during exercise with correlations of 1.00 for cycling, 0.98 for running and weightlifting, and 0.96 for outdoor cycling, though it experiences occasional interruptions where heart rate detection stops. Sleep stage tracking ranks among the top five devices with 80% deep sleep, 83% light sleep, and 67% REM sleep conformity, while nighttime HRV measurements show excellent performance. GPS tracking scores 75 with notable smoothing issues that cause paths to pass through buildings and fences, performing slightly worse than the Ultra 4.
These notes were generated by AI and may contain inaccuracies.
The testing began with heart rate tracking during exercise using the Polar H10 ECG chest strap as the reference device. For stationary cycling, the Apple Watch Series 12 achieved a correlation coefficient of 1.00, with individual cycling sessions showing an almost perfect match between the reference device and the watch, with only minor deviations.
For running, the correlation was 0.98, though with some anomalous measurements. The first running round showed a slight deviation at the beginning, while the second round exhibited greater deviation, particularly at the start, with moments of disconnection where heart rate detection stopped. The third round was essentially perfect. The first two rounds occurred up until September 24th, after which performance appeared much better starting September 25th. The original software was used on the Series 12 without trial versions.
Outdoor cycling showed a lower correlation of 0.96, with some points detecting approximately half of the actual heart rate. Multiple bike tours revealed interruptions as a recurring issue, with some rides showing many interruptions while others were almost perfect. The device typically does not detect the wrong heart rate, but rather stops detecting heart rate altogether during problematic moments. Later rounds appeared better, suggesting a possible firmware update.
Weightlifting proved extremely challenging due to pressure on the wrist when lifting weights. Despite this, a high correlation of 0.98 was achieved. However, occasional moments of disconnection occurred, with the watch not detecting heart rate peaks during certain weightlifting sessions, resulting in straight lines where heart rate detection stopped.
The Apple Watch Series 12 was compared using correlation values across different exercises. For indoor cycling, the correlation of 1.00 outperformed 92% of devices. Outdoor cycling achieved 0.96, placing it at the 71st percentile. Running achieved 0.98 at the 65th percentile. Weightlifting achieved 0.98 at the 91st percentile, though with the asterisk regarding disconnection issues. An objective heart rate tracking score of 98 was calculated for cardio workouts, with the note about interruptions.
All-day heart rate tracking showed a good correlation of 0.99 with the reference device, though with some moments of deviation. The frequency at which measurements are saved appears relatively low, resulting in straight lines between data points. The watch is supposed to measure heart rate more frequently, but it is unclear if all data is being saved in the Apple Health app.
Sleep stage tracking was tested using the Z-Max EEG headband as the reference device. Deep sleep conformity was approximately 80%, light sleep conformity was 83%, and REM sleep conformity was approximately 67%, with a large portion predicted as wake time. This lower REM conformity primarily came from one specific night. Typical nights showed good compatibility between the reference device and the Series 12 for deep sleep detection, with very good congruence in REM sleep periods.
The Apple Watch Series 12 ranked among the top five device brands for sleep stage tracking, alongside Google (Fitbit and Pixel devices), Whoop, Oura Ring 4, and the Eight Sleep Pod. The sleep stage tracking score was calculated as 77, representing the average across individual sensitivities.
Nighttime heart rate measurements showed generally consistent results, though with some strange spikes where the watch detected very high heart rates. The average heart rate over each night across 10 tested nights showed a good match with a maximum deviation of one beat per minute. Heart rate variability measurements demonstrated excellent performance with a very good correlation between the reference device and the Series 12, showing a really good match when plotted side by side.
GPS tracking was tested by running the same route multiple times. The first run showed good overall performance with some deviation near a large wall. The satellite view revealed smoothing that made the path pass through fences and around a pond. Multiple runs showed consistent patterns with greater deviation on the right side near the wall. The Ultra 4 performed better, which is expected given its design for superior GPS tracking.
Cycling GPS tracking across five return trips from work showed good consistency overall. Some signals passed through the middle of roundabouts due to wall interference from nearby large buildings. Multiple bike rides to work revealed smoothing around corners that made routes pass through buildings. The performance was consistent but showed the characteristic Apple smoothing technique.
A GPS tracking score of 75 was assigned, indicating good but borderline performance. The Series 12 performed slightly worse than the Ultra 4, with the smoothing technique being a notable concern. The overall conclusion noted excellent sleep tracking, very good nighttime heart rate variability tracking, reliable overall heart rate tracking with some odd errors, and excellent heart rate tracking during exercise with interruptions. More interruptions occurred than with the Ultra 4, likely due to wearing the Series 12 on the dominant right wrist versus the Ultra 4 on the left wrist.
The reviewer chose to keep both watches on the same wrist throughout testing rather than alternating daily, which made it easier to maintain consistent placement and tracking conditions.
The reviewer raises several open questions about the observed heart rate variability interruptions:
- Whether these interruptions represent a general characteristic of the new sensor before any software updates
- Whether the issue is specific to their individual unit
- Whether the interruptions relate to their particular physiology
- Whether the right wrist placement contributes to more frequent interruptions compared to left wrist placement
Viewers are invited to share their experiences in the comments, particularly those with the new sensors who may be experiencing similar interruptions or those achieving perfect performance with the Ultra 4 or Series 12.
The reviewer recommends several devices for those considering the Apple Watch Series 12 or Ultra 4:
- Apple Watch Series 12
- Apple Watch Ultra 4
- Whoop
- Eight Sleep Pod (described as their favorite sleep-enhancing device)
Affiliate links are provided both below and above the content, offering the best available discounts while supporting the channel at no additional cost to viewers. A general Amazon affiliate link is also available at the bottom that works for any purchase, including small items like toilet paper or coffee beans.
For viewers interested in the Apple Watch Series 12 content, the reviewer suggests two related videos:
- A video about Apple's new sleep-stage tracking algorithm
- A video about the new Eight Sleep Pod 6, which offers better sleep-stage tracking
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