Apple Watch SE 3 Review: An 18-Hour Rating With No Night

Apple's 18-hour figure comes from a scripted day of time checks, notifications, a little app use and a one-hour workout with music. The Series 12 runs the same script, down to the 300 time checks and 90 notifications. Apple then adds six hours of sleep tracking, and that's how it reaches 24. That makes the gap between the two ratings one night of sleep.

Sleep score, sleep apnea alerts and nightly wrist temperature all need the watch on your wrist in bed. An 18-hour rating does not cover a full day and night. Actual runtime varies with use, so plan charging around the nights you want to record.

Eight minutes on the charger covers up to 8 hours of sleep tracking, Apple says, and 15 minutes gives up to 8 hours of normal use. Plan on a short charge every evening while you get ready for bed. If you won't do that, you'll lose the best health features on this watch. The Series 12 gets up to 10 hours of sleep tracking from 5 minutes, a better figure that still asks for the same habit.

The box has Apple's USB-C charging cable but no power adapter, and Apple's charge times come from a 20 W adapter. Buy one if you don't own one, because the whole routine depends on those short charges. Low Power Mode is rated at 32 hours, and that figure does include six hours of sleep tracking. Save it for a weekend away from a charger.

Apple rates an outdoor run at up to 7 hours with the iPhone left at home, three fewer than the Series 12. If you'd rather charge every week or two, Amazfit rates its Bip 6 at up to 14 days of typical use, a different charging schedule for anyone who dislikes a daily top-up.

Sleep apnea notifications run in the background once you've set them up. The watch uses its motion sensor to estimate breathing disturbances overnight, then checks the results in 30-day blocks. Apple's current support page still requires at least 10 nights of recordings in each 30-day period. Set up Track Sleep with Apple Watch as well as the apnea notifications before relying on that background check.

The FDA cleared the feature in September 2024, and its summary reports Apple's study. Apple enrolled 1,499 people, and 1,278 counted toward the alert results. Just under two in three people with moderate to severe sleep apnea got an alert. Among people with normal breathing or mild apnea, about 15 in 1,000 got one wrongly, and none of those wrong alerts went to someone with normal breathing.

Apple chose that balance on purpose, because a check that repeats every month can pile up false alarms. The same FDA table lists the first version of Samsung's feature, which flagged more true cases and more people wrongly. That came from a different study using two days of blood oxygen data, so it isn't a head-to-head result.

No alert doesn't mean you're clear, and the FDA-cleared wording says so: the absence of a notification isn't meant to show the absence of sleep apnea. Apple's current instructions make the feature available from age 18 to people without a sleep apnea diagnosis, and it isn't meant to diagnose anything. If your sleep worries you, talk to a doctor whatever the watch says. Count these alerts as a bonus on Apple's cheapest watch, because they can miss about one case in three.

Apple's comparison table marks four health features as missing from the SE 3: the ECG app, the Blood Oxygen app, hypertension notifications and the Readiness app. The ECG is the one worth paying for, because you can take a reading when you feel something odd. On the SE 3 you get passive alerts for irregular rhythm and for high and low heart rate. Apple also says the irregular rhythm alerts aren't meant for anyone already diagnosed with atrial fibrillation, so discuss monitoring needs with your clinician if you have that diagnosis.

Blood oxygen isn't worth paying for, because Apple calls that app a wellness feature and not a medical one, and you view the results on your iPhone. The Series 12 also has Audio Intelligence, but Live Rewind and Siri Recap need an iPhone 16 or later, so on an older phone it adds little.

The Series 12's screen peaks at 2,000 nits to the SE 3's 1,000, and its wide-angle panel is easier to read from the side. Its case is a millimeter thinner, and it charges faster. We wouldn't pay the difference for those.

Choose the case size after measuring your wrist. This review covers the 40 mm GPS version with a Sport Band. Apple's images on this page show other band styles. The 44 mm has a display area of 977 sq mm, nearly the same as the 970 sq mm on a 42 mm Series 12. The 40 mm's is 759 sq mm, so the bigger case gives you more than a quarter more screen.

Apple says the 40 mm fits wrists from 130 to 200 mm and the 44 mm from 140 to 245 mm. The 40 mm is the better pick for a small wrist, or if you'd notice extra weight in bed: it weighs 26.3 g to the 44 mm's 32.9 g. Both are 10.7 mm thick. Apple sells the Sport Band in S/M and M/L, so measure your wrist before you order.

Both sizes are water resistant to 50 m, which Apple limits to shallow-water use such as swimming in a pool or the ocean. Apple adds that the rating can fade over time.

The SE 3 needs an iPhone 11 or later, or a second-generation iPhone SE or later, running iOS 27. There's no Android option.

Siri AI needs an Apple Intelligence iPhone nearby, Apple says, which means an iPhone 15 Pro or any iPhone 16 or later. It's a beta in watchOS 27, it starts in English, and it has daily usage limits, with expanded access coming for a fee. Workout Buddy needs the same iPhone plus Bluetooth headphones. We wouldn't upgrade a phone for either, because everything else in this review works without them.

The GPS model tracks a run on its own. Calling for help is another matter. Apple says Emergency SOS needs a cellular connection or Wi-Fi Calling, from the watch or an iPhone nearby. So a hard fall on a phone-free run, away from Wi-Fi, can't reach anyone. If that's your routine, pay for GPS + Cellular, which also needs a carrier plan. Check the Fall Detection mode before you rely on it, including whether it covers all-day activity or only workouts.