Between the T-Rex 3 and Watch S4, the T-Rex 3 comes out ahead in battery life and water resistance, while the Watch S4 wins on weight and peak brightness. Overall, the T-Rex 3 scores 79.7 and the Watch S4 scores 63.9 on our Mars Score.
Which should you buy?
The T-Rex 3 is the clear pick on raw spec strength, leading by 15.8 points on the Mars Score. The margin is wide enough that the underdog only makes sense if its individual strengths line up with what you specifically need.
Pick the T-Rex 3 if your top frustration with your current device is running out of charge before the day ends — endurance is the lead spec here. The biggest gaps in its favor are battery life, water resistance, display size.
Pick the Watch S4 if the display is what you stare at all day — refresh rate, brightness, or sharpness is where the difference will be most visible. Its strongest claims are weight, peak brightness, ecg, among others.
Both ship with comparable spo2, so those specs don't separate the two — focus on the differences below.
Bottom line: the T-Rex 3 is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Why Amazfit - T-Rex 3 wins
- ▲Battery life — 86.67% more. 672 h vs 360 h.
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
- ▲Display size — 4.90% more. 1.5 " vs 1.43 ".
Why Xiaomi - Watch S4 wins
- ▲Weight — 24.00 g less. 44 vs 68.
- ▲Peak brightness — 10.00% more. 2200 nits vs 2000 nits.
- ▲Has ECG.
- ▲Has Cellular.
Spec comparison
Design
| Spec | Amazfit - T-Rex 3 | Xiaomi - Watch S4 |
|---|---|---|
| Case size | 48.5 mmlead | 47 mm |
| Weight | 68 g | 44 glead |
| Case material | polymer | stainless steel |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Amazfit - T-Rex 3 | Xiaomi - Watch S4 |
|---|---|---|
| Display size | 1.5 "lead | 1.43 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 2000 nits | 2200 nitslead |
Health & Fitness
| Spec | Amazfit - T-Rex 3 | Xiaomi - Watch S4 |
|---|---|---|
| ECG | false | truelead |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Amazfit - T-Rex 3 | Xiaomi - Watch S4 |
|---|---|---|
| Battery life | 672 hlead | 360 h |
| GPS | true | true |
| Cellular | false | truelead |
| NFC | false | truelead |
| OS | Zepp OSlead | HyperOS |
Frequently asked
Which has longer battery life, T-Rex 3 or Watch S4?+
T-Rex 3 lasts 672h vs 360h.
Do T-Rex 3 or Watch S4 support ECG?+
Watch S4 supports ECG; T-Rex 3 does not.
Which has cellular, T-Rex 3 or Watch S4?+
Watch S4 offers a cellular variant; T-Rex 3 is Wi-Fi only.
Spec-level deep dives
More from the same brands
vsMars is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you. Learn more.