Withings ScanWatch 2: Sleep Tracking Data and Specifications

Data Sources and Methodology

This review compiles data from peer-reviewed research, manufacturer specifications, FDA regulatory filings, and aggregated user reports. No first-person testing was conducted. All sleep accuracy figures reference polysomnography (PSG) comparison data.

The primary accuracy data comes from Schyvens et al. (2025)Cited studyA performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnographySchyvens AM et al. · Sleep Advances · 2025Single most editorially important study in the CircaTest corpus. Six commercial wearables tested against PSG in a uniform protocol means the kappa values are directly comparable in a way most validation studies are not. Drives the head-to-head accuracy figures across CircaTest's comparison content. Limitations: tested previous-generation models (Series 8 not 10, Charge 5 not 6, original ScanWatch not 2) so the results are upper bounds for current models, not direct evidence.View full record →, published in Sleep Advances, which tested the ScanWatch against PSG alongside five other consumer devices. FDA clearance information comes from the public 510(k) record. Hardware specifications are from Withings' published product page. Pricing was verified as of March 31, 2026.

Sleep Tracking Accuracy

Schyvens et al. (2025)Cited studyA performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnographySchyvens AM et al. · Sleep Advances · 2025Single most editorially important study in the CircaTest corpus. Six commercial wearables tested against PSG in a uniform protocol means the kappa values are directly comparable in a way most validation studies are not. Drives the head-to-head accuracy figures across CircaTest's comparison content. Limitations: tested previous-generation models (Series 8 not 10, Charge 5 not 6, original ScanWatch not 2) so the results are upper bounds for current models, not direct evidence.View full record → tested the ScanWatch against PSG, finding a Cohen's kappa of 0.22 — the lowest among six devices tested. The ScanWatch uses a three-stage classification that combines deep and REM sleep into one category, making direct four-stage comparison with other devices difficult. The study reported 94% sensitivity but 31% specificity, indicating the device is prone to classifying wake time as sleep.

The device provides a nightly sleep score, and all sleep staging data is available without a subscription. The ScanWatch 2 also includes a smart alarm feature.

Buyers who prioritize detailed four-stage sleep classification accuracy should weigh this data carefully: the ScanWatch's three-stage model is a different approach than most competitors, and in the SchyvensCited studyA performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnographySchyvens AM et al. · Sleep Advances · 2025Single most editorially important study in the CircaTest corpus. Six commercial wearables tested against PSG in a uniform protocol means the kappa values are directly comparable in a way most validation studies are not. Drives the head-to-head accuracy figures across CircaTest's comparison content. Limitations: tested previous-generation models (Series 8 not 10, Charge 5 not 6, original ScanWatch not 2) so the results are upper bounds for current models, not direct evidence.View full record → comparison it produced the weakest agreement with clinical measurement.

Sensor Suite

The Withings ScanWatch 2 includes seven sensor types:

• PPG (photoplethysmography): Optical heart rate sensor for continuous monitoring
• Accelerometer: Motion detection for sleep-wake classification
• Temperature sensor: Wrist temperature monitoring
• SpO2 (blood oxygen): Blood oxygen measurement, marketed as enabling detection of breathing disturbances
• ECG (electrocardiogram): Single-lead ECG for heart rhythm recording (AFib detection)
• Altimeter: Barometric altimeter
• GPS: Satellite positioning

The sensor count matches the Apple Watch Series 10 as the most extensive among devices reviewed. The device does not include EDA (electrodermal activity) sensors.

Health Features

The Withings ScanWatch 2 tracks:

• Heart rate variability (HRV): Overnight measurement
• Resting heart rate: Continuous monitoring
• Respiratory rate: Estimated from overnight sensor data
• Blood oxygen: Overnight SpO2 monitoring
• Body temperature: Wrist temperature tracking
• ECG and AFib detection: FDA 510(k) cleared

The ScanWatch 2 holds FDA 510(k) clearance K201456 (October 2021), which clears the device for ECG-based AFib detection and SpO2 measurement. Important nuance: K201456 is not specifically a sleep apnea screening clearance. Withings markets the SpO2 function as enabling detection of nighttime breathing disturbances, but the FDA clearance language covers ECG for AFib and SpO2 measurement, not a dedicated sleep apnea screening indication. Buyers who specifically want an FDA clearance scoped to sleep apnea screening should note this distinction (the Apple Watch received De Novo authorization specifically for sleep apnea notification in September 2024).

The device does not offer menstrual cycle tracking, stress tracking, readiness scores, strain tracking, or recovery scores.

Hardware and Form Factor

The Withings ScanWatch 2 weighs 52.6 grams (42mm case, without band). Key specifications:

• Battery life: Up to 35 days per charge
• Water resistance: 50 meters (5ATM)
• Material: Stainless steel case with sapphire glass crystal
• Display: Always-on hybrid analog/digital display

The up-to-35-day battery life is the longest among devices reviewed by a wide margin. This eliminates the daily charging requirement and provides uninterrupted continuous tracking for over a month.

The traditional watch design with analog hands and a small digital sub-dial gives the ScanWatch 2 a conventional appearance that differs from typical fitness tracker aesthetics. The stainless steel and sapphire glass construction is more premium than polymer-based alternatives but contributes to the 52.6-gram weight, which is still substantially heavier than ring-form competitors.

Cost of Ownership

The Withings ScanWatch 2 uses a one-time purchase model:

• Hardware: $350
• Subscription: None required. All features included.

All health features, including ECG and SpO2, are available without ongoing fees.

Two-year cost: $350 (no additional fees)

Pricing verified as of March 31, 2026.

Compatibility

The Withings ScanWatch 2 has broad platform compatibility:

• iOS: Supported
• Android: Supported
• Apple Health: Syncs
• Google Fit: Syncs
• Strava: Syncs

No platform lock-in. The device works with all major mobile platforms and health data ecosystems.

Limitations

Several data points are worth noting:

• Lowest PSG agreement in independent testing: Cohen's kappa of 0.22 (Schyvens 2025Cited studyA performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnographySchyvens AM et al. · Sleep Advances · 2025Single most editorially important study in the CircaTest corpus. Six commercial wearables tested against PSG in a uniform protocol means the kappa values are directly comparable in a way most validation studies are not. Drives the head-to-head accuracy figures across CircaTest's comparison content. Limitations: tested previous-generation models (Series 8 not 10, Charge 5 not 6, original ScanWatch not 2) so the results are upper bounds for current models, not direct evidence.View full record →) was the weakest of six devices tested. For users who prioritize sleep stage accuracy, this is a significant consideration.
• Three-stage sleep model: The device combines deep and REM sleep into a single category, unlike the four-stage breakdown most competitors use
• FDA clearance scope: K201456 covers ECG (AFib) and SpO2, not a dedicated sleep apnea screening indication. Marketing language and clearance language should not be conflated.
• No menstrual cycle tracking: Despite having a temperature sensor, the device does not offer cycle prediction
• No readiness, strain, or recovery metrics: The ScanWatch 2 does not contextualize sleep data within an activity or recovery framework
• No stress tracking: Does not offer daytime or nighttime stress metrics
• Weight: At 52.6 grams, substantially heavier than ring alternatives (2.3-6 grams)

Who the Data Profile Suggests This Fits

Based on the specifications and available data, the Withings ScanWatch 2's data profile aligns with:

• Users who want the longest possible battery life to avoid charging interruptions
• Users who prefer a traditional watch appearance rather than a fitness tracker or tech-forward design
• Users who want ECG-based AFib detection and continuous SpO2 measurement
• Users who value full cross-platform compatibility (iOS and Android, all major health platforms)
• Users who want all features included with no subscription

The device's data profile is less aligned with users who prioritize four-stage sleep classification accuracy, users who specifically want an FDA sleep apnea screening clearance (consider Apple Watch's De Novo authorization instead), or users who need a readiness/recovery framework integrated with their sleep data.