Device research record
Apple Watch Series 8
Signals and sensors
From the device record. Fields the source does not state are left out.
- Maker
- Apple
- Form factor
- Wrist
- Series
- Series 8
- Family
- Apple Watch
- Signals recorded
- PPG, Accelerometer, ECG
- Also called
- Watch Series 8, Apple Watch S8
What published studies show
Results quoted from 6 published validation studies, each against a clinical reference. A result applies to the model and protocol tested, not to every model the brand sells. From the wearable accuracy database (v1.0.0).
Heart rate during exercise1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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/H10) | n = 28, Rest, cycling, recovery | Mulholland et al. (2026)Independent |
- Apple Watch Series 8Skin pigmentation did not predict error (P = 0.62); 50% of missing data from dark-skin participants
Study finding (no single number) · vs ECG chest strap (Polar H7/H10) · n = 28, Rest, cycling, recovery
Mulholland et al. (2026) Independent
Sleep stages (4-stage)3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 |
| Apple Watch Series 8 | κ = 0.3Cohen's kappa | Polysomnography (PSG) | n = 26, Two Korean sleep centres, in-lab PSG | Lee et al. (2023)Independent |
| Apple Watch Series 8 | 56.4%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 26, Two Korean sleep centres, in-lab PSG | Lee et al. (2023)Independent |
- Apple Watch Series 8κ = 0.53
Cohen's kappa · vs Polysomnography (PSG) · n = 62, Sleep laboratory, 1 night
Schyvens et al. (2025) Funding not reported
- Apple Watch Series 850.5–86.1% (range across stages)
Sensitivity · vs Polysomnography (PSG) · n = 35, Inpatient, 1 night
Robbins et al. (2024) Other maker funded
- Apple Watch Series 8Deep sleep −43 min
Mean bias (signed), deep sleep duration · vs Polysomnography (PSG) · n = 35, Inpatient, 1 night
Robbins et al. (2024) Other maker funded
- Apple Watch Series 8κ = 0.3
Cohen's kappa · vs Polysomnography (PSG) · n = 26, Two Korean sleep centres, in-lab PSG
Lee et al. (2023) Independent
- Apple Watch Series 856.4%
Epoch-by-epoch agreement · vs Polysomnography (PSG) · n = 26, Two Korean sleep centres, in-lab PSG
Lee et al. (2023) Independent
Sleep vs wake (2-stage)2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 8> 90% (all devices)
Sensitivity · vs Polysomnography (PSG) · n = 62, Sleep laboratory, 1 night
Schyvens et al. (2025) Funding not reported
- Apple Watch Series 8≥ 95%
Sensitivity · vs Polysomnography (PSG) · n = 35, Inpatient, 1 night
Robbins et al. (2024) Other maker funded
Blood oxygen (SpO2)1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 8 | Met ISO RMS ≤ 4% at normoxia and SpO2 < 90%; lowest bias and RMSD of the threeStudy 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 |
- Apple Watch Series 8Met ISO RMS ≤ 4% at normoxia and SpO2 < 90%; lowest bias and RMSD of the three
Study finding (no single number) · vs Medical-grade pulse oximeter · n = 18, Induced hypoxemia (FiO2 14%, 12%, 10%), ISO 80601-2-61
Walzel et al. (2023) Independent
Energy expenditure (calories)1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 |
- Apple Watch Series 8+21.6 kcal
Mean bias (signed), physical activity energy expenditure, 10 min · vs Indirect calorimetry · n = 52, 10-min recumbent cycling intervals
Kostrna et al. (2026) Independent
Comparisons
Head-to-head pages that name Apple Watch Series 8 come first, then other comparisons for the brand.
- Whoop vs Apple Watch: What the Sleep-Lab Studies FoundMentions Apple Watch Series 8
- Fitbit vs Apple Watch: PPG Sensor Accuracy and Health FeaturesMentions Apple Watch Series 8
- Oura Ring vs Apple Watch: Finger PPG vs Wrist PPG AccuracyMentions Apple Watch Series 8
- Withings vs Apple Watch: ScanWatch 2 ECG, SpO2 and PPG ComparedMentions Apple Watch Series 8
- Garmin vs Apple Watch: PPG, ECG & Battery Compared
- Apple Watch Ultra 2 vs Garmin Fenix 8: Specs Guide
- Samsung Galaxy Watch vs Apple Watch: PPG Sensor and Health Features
- Google Pixel Watch vs Apple Watch: PPG Sensor and Health Ecosystem