Device comparisons
Withings ScanWatch vs Apple Watch: Sleep Accuracy in a Published Study
The published head-to-head result is sleep staging, and it used the original ScanWatch, not ScanWatch 2. Battery life below is Withings’ specification, not a study.
Published study results
| Metric | Withings ScanWatch 2 | Apple Watch Series 10 |
|---|---|---|
| Sleep stagesCohen's κ vs polysomnographySchyvens et al. 2025, n=62 | 0.22Original ScanWatch | 0.53Apple Watch Series 8Closer in this study |
Each row is one statistic from a study already cited on this page. The link names the sample size when this page already states it. This is not a new measurement.
Devices
Withings ScanWatch 2, 42 mm black: product photograph from Withings. Apple Watch Series 10, jet black aluminum with a black sport band: product photograph from Apple Newsroom, September 2024.
At a glance
Schyvens et al. 2025 tested six devices against polysomnography in 62 adults. The Withings device in that study was the original ScanWatch, not ScanWatch 2.
| Specification | Withings ScanWatch 2 | Apple Watch Series 10 |
|---|---|---|
| Sleep stagesCohen's κ vs polysomnography | 0.22Original ScanWatch | 0.53Apple Watch Series 8Closer in this study |
Primary rows only. The study tables further down list more results from the accuracy database.
Hardware specs
| Specification | Withings ScanWatch 2 | Apple Watch Series 10 |
|---|---|---|
| Battery LifeDiffers | About 30 days | Up to 18 h; 36 h Low Power Mode |
| Water ResistanceDiffers | 5 ATM (50 m) | 50 m (ISO 22810:2010) |
| ECG | Yes | Yes |
| SpO2Differs | Yes | Blood Oxygen app (not for medical use) |
Hardware only. Study results are not repeated in this table. Differs marks values that are not the same. An em dash means this page did not publish that figure.
Specs verified on October 26, 2026: Withings ScanWatch 2 product specifications, Withings Support: ScanWatch 2 battery life, Schyvens et al. 2025, Sleep Advances (six devices vs PSG, n=62), Støve et al. 2023, Respiratory Care (SpO2 in COPD), Apple Watch Series 10 technical specifications, FDA De Novo DEN180042: Apple irregular rhythm notification.
Pros and cons
Withings ScanWatch 2
Pros
- About 30 days battery (Withings)
- ECG, SpO2 and 24/7 temperature tracking
- 5 ATM water resistance
Cons
- Original ScanWatch sleep-stage κ 0.22 (Schyvens 2025)
- Small PMOLED screen rather than a full smartwatch display
Apple Watch Series 10
Pros
- Sleep-stage κ 0.53 for Series 8, highest of six devices (Schyvens 2025)
- ECG app and FDA-authorized irregular rhythm notifications
- Full smartwatch apps and display
Cons
- Up to 18 hours battery
- iPhone only
What published studies show
One table per metric. These rows come from the accuracy database and are not repeated as a second card list. From the wearable accuracy database (v1.0.0).
Heart rate at rest3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings ScanWatch | MAPE < 10% in all domains except shopping (10.8%); < 5% when sedentaryStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 7, 12-h free-living | Giggins et al. (2022)Independent |
| Apple Watch Series 9 / Ultra 2 | 5.91% (MAE 3.73 bpm)Mean absolute percentage error | Polar H10 + Kubios HRV | n = 39, Serial morning measurements over 14 days, 316 readings | O'Grady et al. (2024)Independent |
| Apple Watch Series 6R-R intervals and BPM at rest | 1.15%Mean absolute percentage error | ECG | n = 78, Lab: rest, talking, movie, before/ | Bonneval et al. (2025)Independent |
Heart rate during exercise10 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings Pulse HR | Good at rest and 2.7 km/h (r ≥ 0.82); poor at higher speeds (r ≤ 0.33)Study finding (no single number) | ECG chest strap (Zephyr BioHarness / | n = 22, Sitting, standing, Bruce treadmill stages 1–4 | Mendt et al. (2025)Independent |
| Apple Watch Series 6 | High agreement in squat, deadlift, cable row (rho > 0.832)Study finding (no single number) | ECG chest strap (Polar H7/ | n = 29, Resistance exercise (5 exercises) | Støve et al. (2022)Funding not reported |
| Apple Watch SE | Significantly lower MAE than Polar Pacer Pro and Galaxy Watch 6Study finding (no single number) | ECG chest strap (Polar H7/ | n = 37, Low/ | Jeong et al. (2026)Independent |
| Apple Watch Series 8 | Skin pigmentation did not predict error (P = 0.62); 50% of missing data from dark-skin participantsStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 28, Rest, cycling, recovery | Mulholland et al. (2026)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 9 | Less accurate for darker skin pigmentationStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 30, 10-min treadmill | Chase et al. (2024)Independent |
| Apple Watch Series 4 | 0.9%–4.3% (range by intensity)Coefficient of variation | ECG chest strap (Polar H7/ | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
4 more results in the database. Heart rate accuracy across devices →
Overnight heart rate1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6 | ICC 0.96Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Apple Watch Series 6 | 1.5 bpm (absolute bias)Mean absolute error | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
HRV (RMSSD)2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 9 / Ultra 2 | 28.88% (MAE 20.46 ms)Mean absolute percentage error | Polar H10 + Kubios HRV | n = 39, Serial morning measurements over 14 days, 316 readings | O'Grady et al. (2024)Independent |
| Apple Watch Series 6 | ICC 0.67Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Apple Watch Series 6 | 22.5 ms (absolute bias)Mean absolute error (absolute bias) | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
Sleep stages (4-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings ScanWatch | κ = 0.22Cohen's kappa | Polysomnography (PSG) | n = 41, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Apple Watch Series 8 | κ = 0.53Cohen's kappa | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Apple Watch Series 8 | 50.5–86.1% (range across stages)Sensitivity | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
| Apple Watch Series 8deep sleep duration | Deep sleep −43 minMean bias (signed) | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6 | 53%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Apple Watch Series 6 | κ = 0.20Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
2 more results in the database. Sleep accuracy across devices →
Sleep vs wake (2-stage)3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings ScanWatch | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Apple Watch Series 8 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Apple Watch Series 8 | ≥ 95%Sensitivity | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
| Apple Watch Series 6 | 88%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
More results (1)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6 | κ = 0.30Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
Blood oxygen (SpO2)8 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings ScanWatch | Highest missingness: 69.5% of attempts successfulStudy finding (no single number) | Medical-grade pulse oximeter | n = 49, Spot readings, with and without chronic pulmonary disease | Jiang et al. (2023)Independent |
| Withings ScanWatch | Met ISO RMS ≤ 4% at normoxia and SpO2 < 90%Study finding (no single number) | Medical-grade pulse oximeter | n = 18, Induced hypoxemia (FiO2 14%, 12%, 10%), ISO 80601-2-61 | Walzel et al. (2023)Independent |
| Withings ScanWatchdetecting clinically significant hypoxia | 68.5% (spec 80.8%)Sensitivity | Medical-grade pulse oximeter | n = 200, Hospital ward, COVID-19 inpatients | Rajakariar et al. (2024)Independent |
| Apple Watch Series 7 | 3.5% (rest)Root-mean-square error | Medical-grade pulse oximeter | n = 36, Rest, COPD outpatients | Støve et al. (2023)Funding not reported |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6 | r = 0.89Pearson correlation | Medical-grade pulse oximeter | n = 265, Spot readings | Spaccarotella et al. (2022)Independent |
| Apple Watch Series 6 | −0.23 (LoA −3.49 to 3.04)Mean bias (signed) | Medical-grade pulse oximeter | n = 265, Spot readings | Spaccarotella et al. (2022)Independent |
7 more results in the database. SpO2 accuracy across devices →
Atrial fibrillation detection4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Withings ScanWatchsmartwatch ECG app, inconclusive tracings counted | 58% (spec 75%)Sensitivity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Withings ScanWatchsmartwatch ECG app, inconclusive tracings counted | 75%Specificity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Apple Watch Series 6smartwatch ECG app, inconclusive tracings counted | 85% (spec 75%)Sensitivity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Apple Watch Series 6smartwatch ECG app, inconclusive tracings counted | 75%Specificity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch + KardiaBand (SmartRhythm 2.0)AF episodes ≥ 1 h | 97.5% episode sensitivity (PPV 39.9%)Sensitivity | Insertable cardiac monitor | n = 24, Ambulatory, 31,348.9 h of recordings | Wasserlauf et al. (2019)Funding not reported |
| Apple Watch (irregular rhythm notification)PPG irregular pulse notification | PPV 0.84 (95% CI 0.76–0.92)Positive predictive value | ECG patch | n = 419297, Siteless pragmatic study; ECG patch after notification | Perez et al. (2019)Maker funded |
1 more result in the database. AFib accuracy across devices →
VO2max estimate3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 10 | 13.2% (MAE 6.79 mL/kg/min)Mean absolute percentage error | Indirect calorimetry | n = 40, Maximal treadmill test (modified Åstrand) | Lambe et al. (2026)Independent |
| Apple Watch | 13.31% (MAE 6.92 mL/kg/min)Mean absolute percentage error | Indirect calorimetry | n = 30, Maximal treadmill test (modified Åstrand) | Lambe et al. (2025)Independent |
| Apple Watch Series 7 | 15.79% (ICC 0.47)Mean absolute percentage error | Indirect calorimetry | n = 19, Graded cycle ergometer test | Caserman et al. (2024)Independent |
Energy expenditure (calories)6 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 9 | Inconsistent across all groupsStudy finding (no single number) | Indirect calorimetry | n = 30, 10-min treadmill | Chase et al. (2024)Independent |
| Apple Watch Series 4 | 13.5%–27.1% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Apple Watch Series 6 | 14.68–24.85% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Apple Watch Series 8physical activity energy expenditure, 10 min | +21.6 kcalMean bias (signed) | Indirect calorimetry | n = 52, 10-min recumbent cycling intervals | Kostrna et al. (2026)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6walking | 19.8% walk / 24.4% runMean absolute percentage error | Indirect calorimetry | n = 20, Outdoor 2-km walk (6 km/ | Le et al. (2022)Independent |
| Apple Watch | Lowest EE error of 7 devices, but no device below 20%Study finding (no single number) | Indirect calorimetry | n = 60, Sitting, walking, running, cycling | Shcherbina et al. (2017)Independent |
Verdict
Pick ScanWatch 2 if month-long battery and an analog look matter most; pick Apple Watch for a full smartwatch and stronger published sleep-staging results. Both record ECG.
Frequently asked questions
Which tracks sleep better: Withings ScanWatch or Apple Watch?
In Schyvens et al. (2025), Apple Watch Series 8 agreed with polysomnography sleep stages at κ 0.53 and the original Withings ScanWatch at κ 0.22.
Can Withings ScanWatch replace a medical pulse oximeter?
No. Wrist SpO2 has measurable error even on validated wearables: in people with COPD, Apple Watch 7 RMSE was 3.5% at rest (Støve 2023). Use a medical oximeter for clinical decisions.
How long does ScanWatch 2 battery last?
Withings says ScanWatch 2 is designed to run 30 days per charge in its sample usage scenario; frequent SpO2, ECG and workouts shorten it.
Device research records
Datasets, papers and validation results for the models named on this page.