Apple Watch Ultra 3 vs Dexcom Stelo
Two devices, the same questions: what does it actually measure, how good is the data, what does it cost to keep using, and who is it for.
Apple Watch Ultra 3
The most capable multi-sensor wristwatch on the market. Strong at ECG, everyday health nudges, GPS accuracy, and app ecosystem — weaker for high-fidelity HRV research than dedicated rings and straps.
Full review →Dexcom Stelo
The first over-the-counter continuous glucose monitor in the US. A 15-day skin-worn sensor that turns a black-box variable — your glucose response to food, stress and sleep — into a graph you can act on.
Full review →| Spec | Apple Watch Ultra 3 | Dexcom Stelo |
|---|---|---|
| Price | Around £799 | Not sold in the UK — Abbott Lingo is the equivalent here, around £120/month |
| Subscription | Optional (Fitness+, some third-party apps) | None (device is single-use) |
| Form factor | 49 mm titanium case, sapphire crystal, action button | Skin-worn sensor, upper arm, 15 days per sensor |
| Battery life | 36 h typical, 72 h low-power | Sensor lifespan 15 days |
| Water resistance | 100 m (WR100 + EN13319 dive) | Yes (shower/swim) |
| Platforms | iOS only (watchOS) | iOS, Android |
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| Metrics tracked |
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| Data quality | GPS and workout HR accuracy are excellent. ECG rhythm classification is FDA-cleared for atrial fibrillation. HRV is sampled sparsely — trend only, not intra-day. | MARD (mean absolute relative difference) in the ~10% range vs venous blood glucose — best-in-class for consumer CGM. Interstitial lag makes rapid spikes appear ~5 minutes late. |
| Ecosystem | Apple Health, HealthKit, Fitness+, Strava, Zwift, Training Peaks and thousands of third-party apps. Data export via Apple Health XML. | Native Stelo app; data export to Apple Health and Google Health Connect. Third-party integrations via Dexcom API and platforms like Levels, Nutrisense and Signos. |
| Privacy | Health data is end-to-end encrypted when iCloud Advanced Data Protection is enabled. Local processing on-device where possible. | Glucose data stored in Dexcom cloud; can be exported as CSV. HIPAA-aligned handling. |
Apple Watch Ultra 3
- Excellent GPS accuracy with dual-frequency L1+L5
- Only major consumer wearable with medical-grade single-lead ECG
- Best-in-class app ecosystem and notifications
- Rugged case, long battery for a smartwatch
- HRV sampled once per day — insufficient for deep recovery analytics
- iPhone-locked; useless with Android
- Heavy on the wrist for sleep tracking
- iPhone users who want one device for training, health and productivity
- Outdoor athletes needing dive/altitude/GPS-grade metrics
- Android users
- People whose main goal is deep sleep/HRV research (see Oura, WHOOP)
Dexcom Stelo
- Otc — no prescription needed for non-diabetics in the US
- 15-day wear, waterproof, minimally invasive
- Turns diet and exercise into an immediate feedback loop
- Best-in-class sensor accuracy in the CGM space
- Not intended for insulin-dependent diabetics (see G7 for that)
- 15-minute readings vs 1-minute on G7 — smoother, less real-time
- Interstitial fluid lags blood glucose by 5–10 minutes
- Metabolic-optimisation users identifying personal glycaemic responses
- Anyone with pre-diabetes or a family history of type 2 diabetes
- People chasing zone-2 fitness or GLP-1 protocol optimisation
- Type 1 diabetics needing dosing decisions from the device
- Users unwilling to wear a visible sensor on the arm
The everyday-carry answer for iPhone users who want one device to cover everything except deep sleep research.
The lowest-friction way to turn glucose into an actionable metric. Non-diabetics should treat it as a 15–30 day learning tool, not a permanent wear.
Other comparisons
Scores reflect our own testing criteria — data quality, what the device measures that matters for healthspan, and total cost of ownership including subscription. Prices are manufacturer list prices and change often; check before buying. Some links are affiliate links, which never affect a score — see our affiliate disclosure.