WHOOP
WHOOP 4.0
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Released 2021-10
Best Fitness Trackers · head-to-head
WHOOP 4.0 vs Xiaomi Smart Band 9
A sourced, side-by-side comparison. WHOOP 4.0 is cheaper at —. Every spec and price links to its source.
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Xiaomi
Xiaomi Smart Band 9
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Full spec sheet
✓ marks the stronger figure where "more" — or "less", for price and weight — is unambiguously better.
| Spec | WHOOP 4.0 | Xiaomi Smart Band 9 |
|---|---|---|
| US price | — | — |
| Brand | WHOOP | Xiaomi |
| Released | 2021-10 | — |
| Form factor | band | band |
| Display | — | AMOLED 1.62in |
| Battery days | 5 | 21 |
| Gps | No | No |
| Spo2 | Yes | Yes |
| Ecg | No | No |
| Subscription required | Yes | No |
| Water resistance (m) | 10 | 50 |
| Release | 2021 | — |
Sources — WHOOP 4.0: dcrainmaker.com (verified 2026-06-15). Xiaomi Smart Band 9: mi.com (verified 2026-07-08).
What's the difference between the WHOOP 4.0 and Xiaomi Smart Band 9?
Where the two actually differ on the specs we track (3 of 8). Matching specs are omitted.
- Battery days: WHOOP 4.0 5 vs Xiaomi Smart Band 9 21
- Subscription required: WHOOP 4.0 true vs Xiaomi Smart Band 9 false
- Water resistance (m): WHOOP 4.0 10 vs Xiaomi Smart Band 9 50
What reviewers say
Sourced tester consensus for each — the "what people who used it think" layer, not just specs.
WHOOP 4.0
Across 3 testing outlets, the Whoop 4.0 earns a consistently positive verdict, with GearJunkie scoring it 8.0/10. Reviewers converge on its accuracy for sleep, strain, and recovery tracking and its tangible impact on users' daily habits, while the recurring subscription cost (up to $30/month, or $239/year) is the main friction point raised. Battery life is reported consistently at around 4 to 5 days across sources. (3 sourced reviews, 3 lab-tested.)
Praised: Accurate sleep, recovery, and strain tracking (validated against gold-standard measures in one study, corroborated by consistency checks and accurate strain/recovery predictions); Meaningful, positive impact on users' lifestyle and habits; Consistent readings when compared against other wearables.
Flagged: Ongoing subscription cost is a sticking point for some users/reviewers.
Xiaomi Smart Band 9
No sourced tester review yet.