Apple Watch SE 3 vs Series 12: Which One Should You Buy?

The Apple Watch SE 3 starts at $229 and the Series 12 at $399, and the gap buys health hardware: ECG, the Blood Oxygen app, hypertension notifications and the Readiness score are all Series-only. Everything that makes an Apple Watch useful day to day — notifications, workouts, Apple Pay, sleep tracking, fall and crash detection, an always-on display — is on both.

What the SE 3 already does

Per Apple's own specifications: an always-on Retina display at up to 1,000 nits, the S10 chip, up to 18 hours of normal use (32 in Low Power Mode) and a 15-minute fast charge worth up to 8 hours, in 40mm or 44mm aluminium, from $229. On the health side it covers sleep tracking with a Sleep score, sleep apnea notifications, wrist temperature sensing, and high, low and irregular heart rate notifications.

That list would have been the flagship two years ago. For most people it is the whole watch.

What only the Series 12 adds

• ECG app — not available on the SE 3.
• Blood Oxygen app — not available on the SE 3.
• Hypertension notifications — not available on the SE 3.
• Readiness — the new recovery score, Series 12 and Ultra 4 only.
• Brighter display: up to 2,000 nits against 1,000, which matters in direct sunlight.
• Longer battery: up to 24 hours against 18, and a faster top-up (12 hours from 15 minutes, against 8).
• The S11 chip and its Audio Intelligence features, plus the new Health Sensing System.

Check both pages yourself: Apple Watch SE and Apple Watch Series 12.

So which one?

Buy the SE 3 if this is a first Apple Watch, a watch for a child or a parent, or a replacement for an ageing Series 4 or 5 — and you have no particular reason to track heart rhythm or blood oxygen.

Buy the Series 12 if you want ECG or blood oxygen specifically, if hypertension notifications are relevant to you, if you are outdoors in bright sun a lot, or if 18 hours is too tight because you track sleep and want a margin.

One honest note: the 18-hour SE 3 rating means charging daily, and sleep tracking plus a workout can push it. If you plan to wear it overnight, the Series 12's extra six hours is worth more than the spec sheet suggests.

Q: Does the Apple Watch SE 3 have an always-on display?
A: Yes, an always-on Retina display at up to 1,000 nits.

Q: Does the SE 3 have ECG or blood oxygen?
A: No. The ECG app, the Blood Oxygen app, hypertension notifications and Readiness are Series-only.

Q: Does the SE 3 detect sleep apnea?
A: Yes — sleep apnea notifications and sleep tracking with a Sleep score are included.

Q: How much more is the Series 12?
A: $399 against $229, a difference of $170.

Either watch runs the iWatchly apps the same way — the features that differ are Apple's health sensors, not what third-party apps can do.