Comparison · Fitness watches · Desk research
Apple Watch SE 3 vs Apple Watch Series 12
Quick Answer
Apple Watch SE 3 (year introduced 2025, Support 125094) is a 40mm or 44mm aluminum watch with the S10 SiP, a 4-core Neural Engine, 64GB, Always-On Retina OLED with LTPO, Ion-X glass, up to 1,000 nits (2 nits minimum), 324×394 / 368×448 at 326 ppi, L1 GPS, 50m swimproof, a temperature sensor, Crash Detection, and Fall Detection. Apple lists up to 18 hours of normal use and 32 hours in Low Power Mode. The ECG app footnote excludes SE models..
The verdict
Apple Watch SE 3 or Apple Watch Series 12 — quote the two manufacturer sheets.
Why: Same-year-class new-buy fork inside Apple Watch, not SE vs Ultra. Both are on Apple’s watchOS 27 list. SE 3 (Support 125094) is 40/44mm aluminum, S10, 64GB, Always-On LTPO OLED at 1,000 nits, temperature sensor, L1 GPS, 50m, Crash/Fall Detection, 18h / 32h Low Power. Apple’s ECG footnote excludes SE. Series 12 is 42/46mm, S11, Health Sensing System, Always-On LTPO3 at 2,000 nits, ECG / Blood Oxygen, 24h / 38h Low Power / 10h outdoor, $399 Newsroom start.
Buy Apple Watch SE 3 if
You want a current Apple Watch that is on watchOS 27, Always-On, and Crash/Fall Detection in 40mm or 44mm aluminum, and you do not need ECG, Health Sensing System, or Series 12’s 24-hour table.
Buy Apple Watch Series 12 if
You want this year’s everyday Series: S11, Health Sensing System, ECG, 42/46mm, and Apple’s 24 / 38 / 10-hour table at the $399 start.
Spec comparison
OEM rows only. SE 3 numbers are from Apple Support 125094. Series 12 numbers are from apple.com/apple-watch-series-12/specs/ and the 9 September 2026 Newsroom post. Cells Apple does not publish stay marked.
| Spec | SE 3 | Series 12 |
|---|---|---|
| Year introduced | 2025 (Support) | 2026 (Newsroom 9 September 2026) |
| Case size(s) | 40mm and 44mm | 42mm and 46mm (ceramic cases 43mm / 47mm tall) |
| Case material | Aluminum (Starlight, Midnight) | Aluminum, titanium, or ceramic |
| Dimensions (44mm / 46mm Al) | 44 × 38 × 10.7mm | 46 × 40 × 9.7mm (Al/Ti) |
| Display | Always-On OLED + LTPO; 40mm 324×394; 44mm 368×448; 326 ppi; up to 1,000 nits; 2 nits minimum | Always-On LTPO3 wide-angle OLED; 42mm 374×446; 46mm 416×496; 326 ppi; 2,000 nits peak; 1 nit minimum |
| Front crystal | Ion-X (Apple: 4x crack resistance footnote) | Ceramic Shield 2 (aluminum); sapphire (titanium and ceramic) |
| Chip / storage | S10; 64-bit dual-core; 4-core Neural Engine; 64GB | S11; 64GB |
| Battery — normal use | Up to 18 hours (July–August 2025 tests) | Up to 24 hours |
| Battery — Low Power / extra | Up to 32 hours Low Power | Up to 38 hours Low Power; 10 hours outdoor workout |
| Fast charge (OEM) | ~80% in about 45 minutes; 15 min ≈ 8 hours | ~80% in about 30 minutes; 15 min ≈ 12 hours |
| Weight (example SKUs) | GPS 44mm 32.9g; GPS+Cellular 44mm 33.0g; GPS 40mm 26.3g | 46mm Al GPS 39.5g; Al GPS+Cellular 38.6g; Ti 44.9g |
| GNSS | L1 GPS (GLONASS, Galileo, QZSS, BeiDou) | Precision L1 GPS |
| Water | 50m (ISO 22810:2010) | 50m (ISO 22810:2010), swimproof as worded by Apple |
| Dust | Not listed on Support 125094 | IP6X |
| Heart rate | Second-generation optical heart sensor | Health Sensing System |
| ECG | Not applicable (Apple compare + ECG footnote excludes SE) | ECG app (Series 4+, excluding SE) |
| Blood Oxygen | Not listed on Support 125094 | Blood Oxygen app (region limits) |
| Temperature | Temperature sensor listed | Temperature sensor class (Apple: Series 8 or later, SE 3, Ultra models) |
| Safety | Emergency SOS, Crash Detection, Fall Detection | Emergency SOS, international emergency calling, Fall Detection, Crash Detection, Last Emergency Call, Check In |
| OS / phone | Support lists iPhone 11 or later / SE 2+ with iOS 26 or later | watchOS 27; iPhone 11 or later / SE 2+, iOS 27 |
| watchOS 27 (Apple list) | Named (SE 3) | Named (Series 9 or later) |
| US start (dated) | Still sold; date apple.com — not invented here | $399 (Newsroom, 9 September 2026) |
Who each watch is for
SE 3 is Apple’s still-sold value Watch that is actually on the watchOS 27 list. Always-On and a temperature sensor are on Support 125094. ECG is not. If 40/44mm aluminum, L1 GPS, and an 18-hour table are enough, this is the current SE URL.
Series 12 is the current everyday Apple Watch. The paid fork versus SE 3 is S11, Health Sensing System, ECG / Blood Oxygen, the 42/46mm case, Ceramic Shield 2 on aluminum, and Apple’s 24 / 38 / 10-hour table.
watchOS 27 — quote Apple
Series 12 Newsroom, 9 September 2026: “watchOS 27 will be available for Apple Watch Series 9 or later, Apple Watch SE 3, and Apple Watch Ultra 2 or later … and requires iPhone 11 or later or iPhone SE (2nd generation or later) with iOS 27 or later.” Both watches in this pair are on that sentence.
ECG and Blood Oxygen
Apple’s SE 3 compare page marks ECG as not applicable. The footnote excludes Apple Watch SE models. Support 125094 does not list a Blood Oxygen app. Series 12 lists ECG and Blood Oxygen. Do not write ECG onto SE 3.
Battery
Copy Apple’s mode names. SE 3: 18h / 32h Low Power; 15 minutes → up to 8 hours (July–August 2025 tests). Series 12: 24h / 38h Low Power / 10h outdoor workout; 15 minutes → up to 12 hours.
Price
$399 is Apple’s published US starting price for Series 12 on 9 September 2026. This page does not invent an SE 3 start price. Date apple.com/apple-watch-se-3/.
Frequently asked questions
Do SE 3 and Series 12 both get watchOS 27?
Yes, as named. Apple’s Series 12 Newsroom (9 September 2026) says watchOS 27 will be available for Apple Watch Series 9 or later, Apple Watch SE 3, and Apple Watch Ultra 2 or later, and requires iPhone 11 or later or iPhone SE (2nd generation or later) with iOS 27 or later.
Does SE 3 have ECG?
Apple’s SE 3 / Series 12 compare page marks ECG as not applicable on SE 3. The ECG footnote excludes Apple Watch SE models. Series 12 lists the ECG app.
Do they share a chip?
No. Support 125094 lists S10. Series 12 tech specs list S11. Do not write Health Sensing System onto SE 3.
What are the battery claims?
SE 3 Support 125094: up to 18 hours of normal use; up to 32 hours in Low Power Mode (July–August 2025 tests). Series 12: up to 24 hours normal / 38 hours Low Power / 10 hours outdoor workout.