Apple Watch Series 12 a new heart sensor inside a familiar case

What is new about the Apple Watch Series 12?

Very little on the outside, quite a lot underneath. Apple has kept the shape, the screen size and the buttons of the Series 11, and put its effort into what it calls the Health Sensing System. The optical heart sensor has been redesigned with larger, more efficient green LEDs, and the electrical sensor used for ECG readings has bigger electrodes. Apple says the result is background heart rate readings every five seconds and heart rate variability (HRV) readings as often as every five minutes. It quotes 60 times more frequent background heart rate readings and 24 times more frequent HRV readings than the Series 11.

That data feeds a new Readiness score, which Apple says is worked out each morning from your recent activity, vitals and sleep, then adjusted through the day. Garmin, Whoop and Oura have offered something similar for years, so this is Apple catching up rather than leading. There is also a new S11 chip, which runs the Audio Intelligence features (Live Rewind, Siri Recap and automatic Shazam), and aluminium models now get Ceramic Shield 2 glass, which Apple says is 60% tougher than the Ion-X glass it replaces. Dark Bronze is the new aluminium finish; this first look covers Space Grey.

How big is it, and how will it wear?

This is the smaller of the two aluminium sizes. Apple lists the 42 mm case at 42 mm tall, 37 mm wide and 9.7 mm deep, with the GPS version weighing 32.2 grams before the strap. Apple says it fits wrists from 130 mm to 200 mm. The 46 mm model is the one to look at if your wrist is above that range or you want more screen: it measures 46 mm by 40 mm at the same 9.7 mm depth.

The always-on OLED display on the 42 mm case has a resolution of 374 by 446 pixels and a peak brightness of 2,000 nits, according to Apple. Water resistance is 50 m under ISO 22810:2010, plus IP6X dust resistance, and Apple rates it for swimming in a pool or the sea down to 6 metres.

What does it run on, and how long does the battery last?

As a smartwatch there is no movement to speak of: the S11 chip with a four-core Neural Engine and 64GB of storage does the work, running watchOS 27. It needs an iPhone 11 or later to set up, so it is not a choice for Android owners.

Apple quotes up to 24 hours of normal use, 38 hours in Low Power Mode and up to 10 hours of outdoor workout tracking. That headline figure is the same as the Series 11. Independent tests vary widely. Macworld recorded 51 hours in one full drain and 40 hours in a second, and concluded that the Series 12 is slightly weaker on average than its predecessor and less consistent. T3 reports roughly 7% battery use per hour of running. Fast charging helps: Apple says 15 minutes gives up to 12 hours of normal use, though Macworld found 30 minutes of charging produced anywhere from 58% to 72%, short of Apple's 80% claim.

How well is it built?

The recycled aluminium case is familiar and, by most accounts, comfortable enough to wear overnight for sleep tracking. Ceramic Shield 2 should make the aluminium versions more resistant to scratches than before. The one build complaint so far comes from Macworld, which reports a hard edge where the glass meets the case on its review sample, something it did not find on the Series 11. It stresses that the edge is not sharp enough to be a hazard, but it is worth checking in a shop if you are particular about finish.

Is it good value against its rivals?

The RRP for the 42 mm aluminium GPS model is £369 on Apple's UK store, the same starting price as the Series 11. The 46 mm aluminium version starts at £419, cellular adds £100, and titanium and ceramic cases start at £649 and £849.

• Google Pixel Watch 5: £399 RRP for the 45 mm Wi-Fi model on the Google Store UK. The obvious alternative if you use an Android phone, since the Series 12 will not work with one.
• Apple Watch SE 3: £219 on Apple's UK store. It keeps the S10 chip, Ion-X glass and an 18 hour battery claim, and lacks the ECG app, blood oxygen app and new Readiness score, but it covers the basics for £150 less.

If you already own a Series 11, there is little here to justify upgrading. If you are coming from a Series 9 or older, the gains in battery life, charging speed and heart data add up.

What is the catch?

Battery life. Even with the S11 chip, Apple only promises a day of normal use, while Garmin and Huawei rivals routinely last several days. T3 calls battery endurance "comparatively poor", and Macworld's results swung by 11 hours between two runs. Some of the headline features are also not finished: Apple says Live Rewind, Siri Recap and other Audio Intelligence features arrive in beta in late 2026, and Siri AI is rolling out in English first. Buy it for the heart tracking and Readiness score that work today, not for the features still to come.

“A better heart sensor in a case you already know, with the same one-day battery promise.”

What do owners say?

Themes from public owner feedback, paraphrased. We never copy Amazon reviews or ratings.

• An early buyer says the battery now lasts through a day and a night of sleep tracking, so it only needs charging in the morning

  9to5Mac, one week later (opens in a new tab)

• After a month, the Readiness score is the most useful addition, but the bezels around the screen are noticeable in bright apps

  Applesfera, 30 days (opens in a new tab)

• Battery life is inconsistent between charges and fast charging falls short of Apple's 80% in 30 minutes claim

  Macworld (opens in a new tab)