Key takeaways
- ECG: a 30-second single-lead trace taken with your fingers on the bezel. It is good at flagging atrial fibrillation and can be exported as a PDF. It cannot see a heart attack, PVCs, or ischemia, and a clean reading does not rule anything out.
- SpO2: an on-demand spot check or an overnight trend from the optical sensor. Motion, cold hands, nail polish, tattoos and a loose band all skew it. This is not continuous clinical pulse oximetry.
- Temperature: skin temperature variation, not core body temperature. Useful for spotting a trend across nights; useless for diagnosing a fever on its own.
- Sleep breathing: a respiratory-disturbance indicator that can prompt you to get a sleep study. It is not a sleep study.
Which ScanWatch should you buy?
For the fullest sensor set, the ScanWatch 2 in 42 mm is the model to buy; if you want sleep, heart-rate and step tracking and will never use an ECG, the ScanWatch Light is the better value, and the steel Horizon and Nova are cosmetic and water-resistance upgrades rather than sensor upgrades. The important caveat up front: nothing in this line is a medical device in the sense people usually mean. It is a screening tool that produces useful trends and the occasional alert, and the section on limits below matters more than any spec row.
What “medical grade” actually means on a wristwatch
Withings holds regulatory clearances in the US and Europe for the ECG feature on its ScanWatch models, and has pursued clearance for sleep-breathing-disturbance detection, with availability varying by region and firmware. What that means in practice: the watch is permitted to record a single-lead ECG and flag possible atrial fibrillation, and it can flag breathing patterns consistent with sleep apnea. It does not diagnose anything. A cleared screening feature is the start of a conversation with a clinician, not the end of one.
The current lineup compared
Figures below are approximate and shift with firmware and region, so confirm the spec sheet for the exact model and market before buying.
| Model | Case sizes | Case material | ECG | Blood oxygen (SpO2) | Skin temperature | Typical battery | Water resistance |
|---|---|---|---|---|---|---|---|
| ScanWatch Light | ~37 mm | Polymer with steel bezel | No | No | No | Up to ~30 days | 5 ATM (~50 m) |
| ScanWatch 2 | 38 mm and 42 mm | Stainless steel | Yes | Yes | Yes (TempTech24/7) | Up to ~30 days; ~7 days with continuous overnight tracking | 5 ATM (~50 m) |
| ScanWatch Horizon | ~43 mm | Stainless steel, rotating bezel | Yes | Yes | No | Up to ~30 days | 10 ATM (~100 m) |
| ScanWatch Nova | ~42 mm, with a smaller variant | Stainless steel, rotating bezel | Yes | Yes | Yes | Up to ~30 days | 10 ATM (~100 m) |
Across the line you are generally looking at market pricing somewhere in the $250–$600 range depending on case size, finish and band. The steel dive-style models sit at the top of that band; the Light sits at the bottom.
ECG, oxygen and temperature: what each one really records
- ECG: a 30-second single-lead trace taken with your fingers on the bezel. It is good at flagging atrial fibrillation and can be exported as a PDF. It cannot see a heart attack, PVCs, or ischemia, and a clean reading does not rule anything out.
- SpO2: an on-demand spot check or an overnight trend from the optical sensor. Motion, cold hands, nail polish, tattoos and a loose band all skew it. This is not continuous clinical pulse oximetry.
- Temperature: skin temperature variation, not core body temperature. Useful for spotting a trend across nights; useless for diagnosing a fever on its own.
- Sleep breathing: a respiratory-disturbance indicator that can prompt you to get a sleep study. It is not a sleep study.
Sizing: measure before you choose a case
Case diameter gets the attention, but lug-to-lug length decides whether a watch looks oversized. As a rough guide, 37–38 mm cases suit wrists of about 13–17 cm, and 42–43 mm cases suit wrists of roughly 15–20 cm. Measure your wrist circumference just below the wrist bone, then check that the lugs do not overhang the flat top of your wrist — if they do, size down.
Band widths are typically 18 mm on the smaller cases and 20 mm on the larger ones, and the bands are quick-release, so swapping between a silicone strap for chores and a leather or mesh strap for the office takes seconds. For overnight tracking, wear the band snug enough that one finger slides under it but no looser: a loose fit is the single most common cause of dropped heart-rate samples and odd SpO2 readings.
Battery, charging and the 30-day claim
The headline figure assumes periodic heart-rate sampling and an analog watch face doing most of the work. Switch on continuous overnight SpO2 and temperature tracking and expect closer to a week. Charging is by a proprietary magnetic dock and takes roughly one to two hours to full — which works out to around a dozen charges a year instead of daily. Practically, that means keeping the dock on the nightstand rather than in another room; if you take the watch off elsewhere, you lose the sleep data for that night.
The app: what is free and what is not
The Withings app stores activity, sleep, heart rate, ECG recordings and SpO2 history on the free tier, syncs to Apple Health and Google Fit, and lets you export reports to share with a clinician. The paid tier, typically around $10 a month or roughly $100 a year, adds deeper cardiovascular insights and coaching-style scoring. You do not need the subscription for the ECG or the basic export, and it is worth checking which advanced metrics are paywalled in your region before committing.
Match the model to your situation
| Your situation | Pick | Why |
|---|---|---|
| Palpitations or known AFib; you want traces to show a doctor | ScanWatch 2, 42 mm | ECG plus overnight SpO2 and temperature trends in one case |
| Snoring, daytime fatigue, suspected sleep apnea | ScanWatch 2 | Sleep-breathing indicator — then book an actual sleep study |
| Small wrist, under about 16 cm | ScanWatch Light or ScanWatch 2 in 38 mm | Shorter case, less overhang, better overnight fit |
| Swimming, snorkeling, wearing it in the shower | Horizon or Nova | 10 ATM instead of 5 ATM |
| You want it to look like a watch in meetings | Horizon or Nova | Analog hands and a small sub-dial rather than a bright screen |
| You refuse to pay a subscription | Any model on the free tier | Core tracking and export stay free |
| Marathon training with pace and GPS | None of these | No built-in GPS; a dedicated sport watch fits better |
| Budget-first, sleep and steps only | ScanWatch Light | You give up ECG and SpO2 and little else |
Where consumer tracking stops
No ScanWatch measures blood pressure — Withings sells separate cuff monitors for that — and none measures blood glucose. There is no continuous ECG, no built-in GPS, and no arrhythmia classification beyond AFib. Optical heart rate drifts during interval work and heavy lifting compared with a chest strap. Regulatory clearances differ by country, so a feature advertised in one market may be absent in yours. If a reading worries you, the correct next step is a clinician, not a second reading.
Straps, durability and household realities
Steel cases scratch, and door frames, furniture edges and cardboard boxes during a move are the usual culprits. Keep a silicone or fluoroelastomer band for gardening, furniture assembly and workshop tasks, and save the leather or mesh for everything else. Both 5 ATM and 10 ATM handle splashes and swimming, but neither is built for hot showers or diving, since steam degrades the seals over time.
Quick answers
- Does it measure blood pressure? No. Use a validated cuff.
- Can it replace a Holter monitor? No — it takes snapshots, not a continuous multi-day trace.
- Does it work with Android? Yes, alongside iOS, though a few features differ by platform.
- Will my doctor use the data? An exported ECG PDF can be useful context, but diagnosis still requires clinical-grade testing.
