A ScanWatch on your wrist and a Sleep pad under your mattress use different sensors, and the Withings app shows HRV from both as the same overnight graph with two 90-minute averages.
Documentation checked: 22 October 2026. Withings updates its app and firmware often, so details can change.
Which Withings devices measure HRV
Withings added HRV in 2025. App version 7.5, released in May 2025, added it for the ScanWatch 2 and, along with breathing rate Breathing rate How many breaths you take a minute. It moves HRV on its own: slower, deeper breathing makes the beat-to-beat swing larger, and below about 9 breaths a minute it shifts from the HF band into LF. More about Breathing rate and night-time movements, for the Sleep and Sleep Analyzer (Withings, release notes 7.0+). Firmware 2871 then let the ScanWatch 2 and ScanWatch Nova “automatically measure your Heart Rate Variability (HRV) overnight”, and brought the same to the ScanWatch Vitals and Healthmaster (Withings Support, FW 2871). Those two are region-specific versions of the ScanWatch 2 and Nova without the ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG ; Withings lists Canada, Japan, Singapore and Thailand as the places to buy the Vitals (Withings Support, Vitals FAQ).
Withings’ pages disagree about the ScanWatch Light. One FAQ says it tracks “overnight Heart-Rate Variance”, but the Light’s own feature list does not mention HRV, and Withings’ developer table of available data marks HRV for the ScanWatch 2 but not for the Light or the original ScanWatch (Withings Support, ScanWatch 2 FAQ and ScanWatch Light; Withings, Available Health Data). We found no Withings page that documents HRV on the original ScanWatch.
The two kinds of device measure in different ways. The watch shines green light into the skin and times each pulse as it arrives at the wrist; the PPG guide explains how. The pad is a pressure sensor that picks up heart rate “using ballistocardiography” (Withings Support, Sleep): it feels the tiny recoil of your body each time the heart pumps blood. Neither records the heart’s electrical signal the way a chest strap does.
From the sensor to the app, and out of it
Measured overnight
- ScanWatch 2, Nova, Vitals or Healthmaster Green light under the watch times each pulse at the wrist.
- Sleep or Sleep Analyzer A pressure sensor under the mattress picks up the body’s tiny recoil with each heartbeat (ballistocardiography).
In the Withings app
Home → last night’s sleep → scroll down
Heart rate variability, ms Simulated night
- Average (first 90 min)
- 43.7 ms
- Average (last 90 min)
- 52.9 ms
Out of the app
- Apple Health, Health Connect HRV is on Withings’ list for Apple Health, which stores HRV as SDNN. Accounts opened on or after 13 October 2026 need Withings+ to export.
- Withings API RMSSD and SDNN samples through the night, and start and end averages, for apps on Withings’ Advanced Biomarkers API plan.
- CSV export Free, but HRV is not on Withings’ list of exported data.
Three columns joined by arrows. The first column shows the two sensors that measure HRV overnight: a ScanWatch, whose green light times each pulse at the wrist, and the Sleep or Sleep Analyzer pad under the mattress, which picks up the body’s recoil with each heartbeat. The second column is a phone screen in the Withings app: the path from the Home tab to last night’s sleep, a line graph of HRV through a simulated night with the first and last 90 minutes of sleep shaded, and two rows under it, Average (first 90 min) 43.7 ms and Average (last 90 min) 52.9 ms. The third column lists three ways out of the app: Apple Health and Health Connect, which need Withings+ for accounts opened on or after 13 October 2026; the Withings API, which gives apps on its Advanced Biomarkers plan RMSSD and SDNN samples and start and end averages; and the free CSV export, whose list of data does not include HRV.
What HRV number Withings shows
The app draws HRV through the night in milliseconds and lists two averages under the graph: “Average (first 90 min)” and “Average (last 90 min)”. Withings’ help pages do not name the formula for either (Withings Support, ScanWatch 2 HRV). Its developer documentation defines two HRV samples, RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD over “a few seconds” and SDNN SDNN The standard deviation of all NN intervals in a recording, in milliseconds. It measures overall variability, and its value depends strongly on how long the recording lasts. More about SDNN over 1 minute, and gives each night an RMSSD “start average” and “end average” (Withings, API reference). That makes RMSSD the likely basis, but the app does not say so.
Withings reads the pair as a verdict: “The higher your average HRV at the end of the night, the more restorative your night was.” The two windows hold different sleep, though. The first 90 minutes usually hold the night’s first deep sleep and the last 90 more REM, and the body clock Circadian rhythm The body's 24-hour clock. Heart rate is lower and vagal HRV higher at night than by day, so readings are only comparable when they are taken at the same time of day. More about Circadian rhythm adds its own rhythm: in one small study, parasympathetic Parasympathetic nervous system The "rest and digest" branch of the autonomic nervous system. It slows the heart, mainly through the vagus nerve, and drives most of the beat-to-beat variation in HRV. More about Parasympathetic nervous system activity in deep sleep peaked around 2 a.m. while sympathetic Sympathetic nervous system The "fight or flight" branch of the autonomic nervous system. It speeds up the heart and makes it pump harder, but it acts too slowly to drive beat-to-beat HRV. More about Sympathetic nervous system activity in REM peaked in the early morning (Boudreau and colleagues, 2013). RMSSD also differs from one sleep stage to the next (Herzig and colleagues, 2018). Part of any gap between the averages comes from the night’s structure, before recovery plays a part. The sleep page covers the stage effects in more detail.
Same night, different numbers
A teaching model, not a measurement
Sleep stages lights out to waking
HRV every 5 minutes (RMSSD) 20 to 60 ms
- Withings
- first 90 min 43.7 ms, last 90 min 52.9 ms (RMSSD)
Two averages under a graph of the whole night: one over the first 90 minutes of sleep, one over the last 90. The app does not name the formula; Withings’ developer documentation names the matching fields after RMSSD.
Same night, same heart: Withings 43.7 then 52.9 ms and Oura 47.5 ms, because each device averages different hours.
The buttons work when JavaScript is on. The window for each device is listed in the description.
Two charts over eight hours of simulated sleep. The top chart is a hypnogram stepping between awake, REM, light and deep sleep, with deep sleep mostly in the first half and REM mostly in the second. The bottom chart is a line of HRV values, one per five minutes, that rise gently through the night and dip during wakeful minutes. One button per device shades the part of the night that device averages. Withings: first 90 min 43.7 ms, last 90 min 52.9 ms (RMSSD). Oura: 47.5 ms RMSSD. Same night, same heart: Withings 43.7 then 52.9 ms and Oura 47.5 ms, because each device averages different hours.
The model above shades both windows on one simulated night next to Oura’s whole-night average. On every simulated night the late average comes out higher than the early one, and the model has no recovery in it: the gap comes from the stage mix and the gentle rise built into the night. The averages also depend on how many samples the watch catches. With Respiratory Scan switched on, Withings’ example graph holds far more points through the night (Withings Support, ScanWatch 2 HRV).
Where to find HRV in the Withings app
On the Home tab, tap any sleep data to open the sleep graph, then scroll down to the HRV graph (Withings Support, ScanWatch 2 HRV). Withings’ HRV pages for the Sleep pads show the same graph. Withings documents HRV only as an overnight measurement in the app; we found no reading you can start yourself.
If the graph has gaps or looks wrong, Withings suggests wearing the watch on your non-dominant wrist, one to two finger-widths from the wrist bone, tight enough not to move; it adds that a metal or leather band “may” give inaccurate HRV (Withings Support, HRV Issues). Where do I find HRV on my device has the same steps for other brands.
Withings Readiness and HRV
The Readiness Indicator gives a daily status, green for high or balanced and red for low, built from Recovery (last night’s sleep), Effort (steps and activity) and Night Vitals (sleep temperature, blood oxygen and breathing rate). Withings needs Recovery and Effort for a status (Withings Support, Readiness). The Readiness help pages do not list HRV as an input. Two other Withings pages do. The September 2025 announcement of the indicator, then called Vitality, said it “combines data from heart rate variability” with activity, temperature, oxygen saturation, breathing and sleep (Withings Support, ScanWatch 2 2025 Edition), and the US store’s ScanWatch 2 page says Readiness is “powered by nightly HRV, temperature, sleep and breathing data” (Withings US store, ScanWatch 2). The store’s Sleep page says “sleep, heart and breathing data” instead.
What is in a readiness score?
From the makers' own documentation
- HRV : named by the maker Named on the US store’s ScanWatch 2 page ("powered by nightly HRV") and in Withings’ September 2025 announcement of the indicator, then called Vitality. The Readiness help pages do not list it.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : named by the maker Respiratory rate, one of the Night Vitals, "when applicable".
- Sleep : named by the maker Recovery, "representing sleep data for the previous night".
- Temperature : named by the maker Sleep temperature, one of the Night Vitals.
- Activity or load : named by the maker Effort, "representing steps and activity data for the day", compared with your average level.
Also: Blood oxygen (SpO2), the third Night Vital. Withings’ release note for app 8.0 also names heart rate, without saying resting heart rate.
Withings's Readiness Indicator names 5 of the six inputs: HRV, breathing rate, sleep, temperature and activity or load. Withings needs Recovery and Effort for a status, treats Night Vitals as optional, and does not say how they are combined.
Source: Withings App: Readiness Indicator (Withings Support)
A list of scores, one per device, with six inputs for each: HRV, resting heart rate, breathing rate, sleep, temperature and activity or load. Withings's Readiness Indicator names 5 of the six inputs: HRV, breathing rate, sleep, temperature and activity or load. Withings needs Recovery and Effort for a status, treats Night Vitals as optional, and does not say how they are combined.
The help pages describe a coloured status rather than a number, and Withings publishes no formula, so you cannot tell how much last night’s HRV moved it. Read the HRV graph as well. Recovery scores explained compares Readiness-type scores across brands.
Is HRV free, or does it need Withings+?
Withings does not list HRV among the Withings+ features, and the HRV graph sits in the sleep view. For the Sleep pad, Withings says: “you’ll always have free, unlimited access to your sleep history and trends” (Withings US store, Sleep); the ScanWatch 2 page says “Your data is always free.” Withings+ adds AI insights and the Health Assistant, the Health Improvement Score, Cardio Check-Up (a cardiologist reviews your ECG within 24 hours) and other services (Withings Support, Withings+; Withings US store, ScanWatch 2).
Withings’ pages differ on Readiness. The help center describes a Readiness screen with extra insights and guidance for subscribers; the US store lists Readiness under Withings+, “Unlocked with 1-Month Free Trial” (Withings Support, Readiness; Withings US store, Sleep).
On the Withings US store on 22 October 2026, Withings+ cost $9.95 a month or $99.50 a year, the ScanWatch 2 (42 mm) $369.95 and Sleep $199.95. Products bought from the Withings web store come with one month of Withings+, and subscribing in the app gives a 2-week trial (Withings Support, Withings+).
Exporting Withings HRV
- CSV export. Free, from Profile → Settings → Export All Health Data, but HRV is not on Withings’ list of exported data (Withings Support, Exporting your data).
- Apple Health. Heart rate variability is on Withings’ list of data the two apps can share (Withings Support, Apple Health). Withings does not say which statistic it writes, and Apple Health stores HRV as SDNN (Apple Developer Documentation), so keep it apart from an Apple Watch’s own readings. Withings notes that Sleep Analyzer heart rate does not sync to Apple Health (Withings Support, sleep heart rate).
- The Withings API. Apps whose developers hold Withings’ Advanced Biomarkers API plan can read the RMSSD and SDNN samples, an HRV quality score, and the start and end averages (Withings, API reference; Available Health Data).
Accounts opened on or after 13 October 2026 need Withings+ to export data to third-party apps such as Apple Health and Health Connect. Accounts that existed before then keep free export, and anyone can download a PDF of their data (Withings Support, AI Connector FAQ and Apple Health).
How accurate is Withings HRV?
We found no peer-reviewed study that compared Withings HRV, from the watch or the pad, with an ECG. Withings’ help pages say HRV accuracy “has now been greatly improved since the release of Withings 7.6”, without publishing data (Withings Support, ScanWatch 2 HRV). The release notes list 7.6 as an August 2025 hotfix for crashes and do not mention HRV (Withings, release notes 7.0+). The device validation tracker has no Withings rows for that reason.
The studies that exist measured other things:
- Heart rate on the first ScanWatch: in 7 adults over 12 hours of daily life, against a Polar H10, the average error was 5.1%, under 5% while sitting and larger during walking, gardening and housework. Sleep produced too little data to analyse (Giggins and colleagues, 2022).
- Heart rate during changes: a Withings ScanWatch did acceptably at steady states and less well when heart rate rose or fell quickly (Van Oost and colleagues, 2025).
- The Sleep Analyzer: studies tested sleep and wake against polysomnography, where it overestimated total sleep by 48 minutes on average (Manners and colleagues, 2025), and sleep apnea detection (Edouard and colleagues, 2021).
Accurate heart rate does not make HRV accurate, because HRV depends on timing each beat to within milliseconds. Is wrist HRV as accurate as a chest strap explains the gap.
How to read your Withings HRV
- Keep two trends. Compare tonight’s early average with earlier early averages, and the late one with earlier late ones. Withings suggests comparing with the previous night; a week or more of nights is a steadier guide.
- Check what changed. Withings lists heavy meals, caffeine and alcohol before bed among the things to avoid for a better night-time HRV. A metal or leather band, the other wrist or an app update can shift the values too.
- Compare Withings only with itself. Its 90-minute averages are not a whole-night average or a morning reading, so they will not match an Oura, Garmin or chest-strap number. HRV by device lists what each brand measures, and normal HRV explains what published values can tell you.
When to talk to a doctor
Withings HRV is not a medical test. Talk to a doctor if low HRV comes with feeling unwell, lasting fatigue, palpitations, dizziness, fainting or chest pain, whatever the number says.
The ScanWatch 2 records a single-lead ECG, and the FDA has cleared Withings’ ECG app (510(k) K240795) to detect atrial fibrillation from it. Withings says the app “does not detect heart attacks or other arrhythmias”, does not provide a diagnosis, and should not be used with a pacemaker Sinus node The heart's natural pacemaker, a small patch of cells that starts every normal heartbeat. Left alone it fires about 100 times a minute; the vagus nerve holds it lower at rest. More about Sinus node , ICD or other implanted electronic device (Withings US store, ScanWatch 2). If the watch flags an irregular rhythm, take that to a doctor. HRV means little during atrial fibrillation, because the beats no longer follow the sinus node; the artifacts guide explains why. For snoring or pauses in breathing at night, see can HRV show sleep apnea.