3Rank 03 of 8 · Best Fitness Trackers
Apple Apple Watch SE 3
The most accurate device in this ranking on both heart rate and sleep staging — and the only one where the sleep chart is worth more than a glance.
8.6BPR score
- €269Price
- MAPE 1.09–1.56%; sleep staging κ = 0.53Measured heart-rate accuracy against an ECG chest strap
- 3 of 8in Best Fitness Trackers
- 8.6BPR score 0–10
Review
What this product is
Written after the analysis, from the same sources the score is built on: the manufacturer's documentation, available studies and verified owner feedback.
If accuracy is the only thing you care about and you own an iPhone, this is the answer.
Validation work puts Apple Watch heart-rate MAPE at 1.09–1.56% across protocols — the tightest range in this ranking. More interesting is sleep: against polysomnography, Apple's sleep-stage agreement reaches Cohen's κ = 0.53, the highest figure published for any consumer wearable. In a category where κ runs from 0.21 upward, that is the difference between a chart worth reading and a decorative one. It is still only "moderate" agreement — nobody has solved wrist-based sleep staging.
You also get a fast-enough processor for the watch to be usable as a watch, crash detection, and the widest third-party app ecosystem here.
The limitations are real and they are structural. It works only with an iPhone — there is no Android path, at all. Battery is around 18 hours, so sleep tracking means charging during the day, which is the opposite of how every other device here works. At €269 it is three times the Fitbit for a measurable but modest accuracy gain. And the SE line omits the blood-oxygen sensor and the always-on display of the full Series.
Technical data
Specification
Figures from the manufacturer's documentation, verified against available outside sources. Values we could not confirm are marked as declared.
- Heart rate
- Optical PPG, third-generation SE
- ECG
- Yes
- Sleep staging
- κ = 0.53 vs polysomnography
- Battery
- ~18 hours
- Compatibility
- iPhone only
- Water resistance
- 50 m
Component scores
Where the score
comes from.
Four components, equal weight, each on a 0–10 scale and each resting on a named source. The overall score is their mean — the full procedure is in the methodology.
What we liked
- MAPE 1.09–1.56% — the most accurate heart rate here
- Sleep staging κ = 0.53, the best published for any consumer wearable
- ECG and crash detection
- The strongest app ecosystem in the category
Worth knowing
- iPhone only — no Android support of any kind
- ~18 hours battery: sleep tracking requires a daytime charge
- €269 — three times the Fitbit for a modest accuracy gain
- No blood-oxygen sensor on the SE line
- No user-replaceable battery
Comparison
How it compares
within the category
All values come from the same analysis and are comparable only within the category Best Fitness Trackers.
| Product | Score | Measured heart-rate accuracy against an ECG chest strap | Price |
|---|---|---|---|
| Fitbit Charge 6Top score | 8.9 | ~1% deviation vs Polar H10 chest strap | €85 |
| Apple Watch SE 3This product | 8.6 | MAPE 1.09–1.56%; sleep staging κ = 0.53 | €269 |
| Category average8 products analysed | 8.2 | — | — |
FAQ
Frequently asked questions
Can I use it with an Android phone?
No. Not partially, not with a third-party app. Apple Watch requires an iPhone for setup and for every sync afterwards.
Is the sleep tracking actually reliable?
More reliable than anything else here, and still not clinical. κ = 0.53 is moderate agreement with polysomnography. Trust the total-sleep figure; treat the four-stage breakdown as an indication of trend, not a measurement.
From the same ranking
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The same protocol, the same key parameter, the same set of sources.
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