Apple Watch Series 12 is two chip generations ahead of the 2023 Series 9, moving from the S9 to the S11, and it adds a new Health Sensing System, a depth gauge, a 24-hour battery rating instead of 18, and 42 mm and 46 mm cases in place of 41 mm and 45 mm, all at the same $399 starting price. A Series 9 still runs watchOS 27, so the question is how much of the new hardware you would miss.
Series 9 launched in September 2023 at $399 with the S9 chip, according to Apple’s press release. Since then Apple has changed the case sizes with Series 10, extended battery life with Series 11 and now replaced the heart sensors with Series 12, which our Series 12 announcement coverage details.
| Key fact | Series 12 (Apple’s tech specs) |
|---|---|
| Price | From $399; $11.99 a month on a 24-month Apple Upgrade lease |
| Chip | S11, 64-bit dual-core, 4-core Neural Engine, Secure Exclave |
| Sizes | 42 mm and 46 mm; ceramic 43 mm and 47 mm |
| Heart sensing | Heart rate every 5 seconds, HRV every 5 minutes |
| Battery | Up to 24 hours; 38 hours Low Power Mode; 10 hours outdoor workout |
| Charging | 80 percent in about 30 minutes; 15 minutes gives up to 12 hours |
Series 12 vs Series 9: every spec that moved
| Spec (Apple’s tech specs and Apple Support) | Series 12 (2026) | Series 9 (2023) |
|---|---|---|
| Chip | S11, 4-core Neural Engine, 64GB | S9, 4-core Neural Engine, 64GB |
| Case sizes | 42 mm, 46 mm | 41 mm, 45 mm |
| Materials | Aluminum, titanium, ceramic | Aluminum, stainless steel |
| Front crystal (aluminum) | Ceramic Shield 2 | Ion-X glass |
| Heart sensors | New optical sensor, third-generation electrical sensor | Previous generation |
| Depth gauge, water temperature | Yes, to 6 m | No |
| Water resistance | 50 m | 50 m |
| Battery | Up to 24 hours | Up to 18 hours |
| Low Power Mode | Up to 38 hours | Up to 36 hours |
| 80 percent charge | About 30 minutes | About 45 minutes |
| watchOS 27 | Yes | Yes |
| Launch price | $399 | $399 |
S9 to S11: the chip and the sensors it runs
On paper the two chips look alike: Apple Support lists the S9 as a 64-bit dual-core system with a 4-core Neural Engine and 64GB of storage, and Apple’s Series 12 tech specs describe the S11 the same way. What Apple highlights instead is the S11’s Secure Exclave, a hardware-isolated compartment for on-device audio processing with immediate deletion.
Don’t miss the best of The Mac Observer
Set us as a preferred source and our Apple reporting ranks higher in your Google Search results and Discover feed — one tap, no account changes.
That compartment enables Audio Intelligence: Sound Recognition alerts for sirens, alarms, doorbells and baby cries, Live Rewind for the previous 15 seconds of conversation as text, Siri Recap summaries and Shazam. Apple’s Series 12 page says Sound Recognition is coming late 2026.
The sensor change is larger. Apple’s press release describes new optical and electrical heart sensors with bigger green LEDs that read heart rate every five seconds all day and HRV every five minutes, split into Recovery HRV and overall HRV. The data drives the new Readiness app, a daily 0 to 10 score with four recommendations. Series 12 also gains the depth gauge to 6 meters and water temperature sensor that arrived with Series 10; Apple Support lists neither for Series 9.
Battery: 18 hours to 24, and 80 percent in 30 minutes instead of 45
Apple Support rates Series 9 at up to 18 hours of normal use, 36 hours in Low Power Mode and about 45 minutes to 80 percent. Apple’s Series 12 specs list up to 24 hours, 38 hours in Low Power Mode, 10 hours of outdoor workout, about 30 minutes to 80 percent, up to 12 hours from a 15-minute charge and up to 10 hours of sleep tracking from 5 minutes.
Sizes, materials and bands: 41/45 mm becomes 42/46 mm
Series 9 came in 41 mm and 45 mm aluminum or stainless steel. Series 12 comes in 42 mm and 46 mm aluminum or titanium, plus a new ceramic case in Pearl White and Night Blue that measures 43 mm and 47 mm and 9.85 mm deep. Aluminum models get Ceramic Shield 2, which Apple says is 60 percent tougher than Ion-X glass, while titanium and ceramic use sapphire crystal.
Both watches peak at 2000 nits with a 1 nit minimum and carry a 50 m water rating, and both keep ECG, Blood Oxygen and the temperature sensor.
What a Series 9 gets from watchOS 27, and what it does not
Series 9 is the oldest Series model on Apple’s watchOS 27 list, so on September 14 it gets Siri AI in beta, the dynamic app grid, the Smart Stack tap gesture, Workout Buddy without a nearby iPhone, and perimenopause and menopause support in Cycle Tracking, the same day iOS 27 arrives on iPhone. Per Apple’s listings, these stay with Series 12:
- The Health Sensing System, five-second heart rate, five-minute HRV and the daytime vitals view.
- Audio Intelligence, tied to the S11’s Secure Exclave.
- The Readiness app and the Steps complication, which Apple lists under Series 12 and Ultra 4.
- Depth gauge features, the ceramic case and Ceramic Shield 2.
What Apple has not said
- Titanium, ceramic and cellular prices for Series 12, and band prices.
- A trade-in value for Series 9; Apple’s Trade In page gives no per-model figure without condition questions.
- Whether Readiness or the Steps complication will come to Series 9 in software.
- How much longer Series 9 will receive major watchOS updates after 27.
Series 12 is on pre-order now from $399 and reaches stores on Friday, September 18, according to Apple’s press release. Apple no longer sells Series 9, and Series 12 sits between the $249 Apple Watch SE 3 and the $799 Apple Watch Ultra 4 in Apple’s current lineup.
