Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Amazfit - T-Rex 3 | Withings - ScanWatch 2 |
|---|---|---|
| Display size | 1.5 " | 0.63 " |
| Weight | 68 g | 59 g |
| Battery life | 672 h | 720 h |
| Water resistance | 10 ATM | 5 ATM |
| ECG | false | true |
| Peak brightness | 2000 nits | 0 nits |
Between the T-Rex 3 and ScanWatch 2, the T-Rex 3 comes out ahead in display size / water resistance, while the ScanWatch 2 wins on weight / battery life. Overall, the T-Rex 3 scores 62.7 and the ScanWatch 2 scores 78.3 on our Mars Score.
Which should you buy?
The ScanWatch 2 is the clear pick on raw spec strength, leading by 15.6 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 the display is what you stare at all day — refresh rate, brightness, or sharpness is where the difference will be most visible. The biggest gaps in its favor are display size, water resistance, peak brightness. The single most decisive one: Display size — 138.10% more. 1.5 " vs 0.63 ".
Pick the ScanWatch 2 if your top frustration with your current device is running out of charge before the day ends — endurance is the lead spec here. Its strongest claims are weight, battery life, ecg. The single most decisive one: Weight — 9.00 g less. 59 vs 68.
Both ship with comparable cellular, spo2, so those specs do not separate the two — focus on the differences below.
Bottom line: the ScanWatch 2 is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Which should you buy: Amazfit - T-Rex 3 or Withings - ScanWatch 2?
Withings - ScanWatch 2 leads the current Mars Score by 15.6 points.The more useful decision is the trade-off behind that result: compare display size, battery life against the way you will actually use the product.
Choose Amazfit - T-Rex 3 if…
Amazfit - T-Rex 3 has the measurable edge on display size in, water resistance atm, peak brightness nits.
Choose Withings - ScanWatch 2 if…
Withings - ScanWatch 2 has the measurable edge on weight g, battery life h, has ecg.
This is a structured comparison of the published catalog values. It is not a claim of identical real-world performance across every workload; use the linked spec drill-downs and methodology page to inspect the inputs.
Why Amazfit - T-Rex 3 wins
- ▲Display size — 138.10% more. 1.5 " vs 0.63 ".
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
- ▲Peak brightness: 2000 nits vs 0 nits.
Why Withings - ScanWatch 2 wins
- ▲Weight — 9.00 g less. 59 vs 68.
- ▲Battery life — 7.14% more. 720 h vs 672 h.
- ▲Has ECG.
Spec comparison
Design
| Spec | Amazfit - T-Rex 3 | Withings - ScanWatch 2 |
|---|---|---|
| Case size | 48.5 mmlead | 42 mm |
| Weight | 68 g | 59 glead |
| Case material | polymer | stainless steel |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Amazfit - T-Rex 3 | Withings - ScanWatch 2 |
|---|---|---|
| Display size | 1.5 "lead | 0.63 " |
| Always-on display | truelead | false |
| Peak brightnessⓘ | 2000 nitslead | 0 nits |
Health & Fitness
| Spec | Amazfit - T-Rex 3 | Withings - ScanWatch 2 |
|---|---|---|
| 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 | Withings - ScanWatch 2 |
|---|---|---|
| Battery lifeⓘ | 672 h | 720 hlead |
| GPS | truelead | false |
| Cellular | false | false |
| NFC | false | false |
| OS | Zepp OSlead | Withings OS |
Frequently asked
Which has longer battery life, T-Rex 3 or ScanWatch 2?+
ScanWatch 2 lasts 720 hours vs 672 hours.
Do T-Rex 3 or ScanWatch 2 support ECG?+
ScanWatch 2 supports ECG; T-Rex 3 does not.
Which has cellular, T-Rex 3 or ScanWatch 2?+
Neither offers cellular.