Apple watch Series 8 and SE review: Both watches could save your life. One could help you make a baby

There’s the updated Apple Watch SE (starting at $249), the Apple Watch Series 8 (starting at $399) and a brand-new model, the Apple Watch Ultra ($799). This review focuses on the first two: the entry-level, second-generation SE and the Series 8 with more advanced health sensors, which I’ve been testing for the past few days. I’ll be reviewing the Ultra, the first Apple Watch with multiday battery life, soon.

For the lower two models, the hardware improvements can possibly save your life. The Series 8 could help you conceive a baby. Still, Apple’s real day-to-day improvements come in WatchOS 9, a free software update also available to some older models.

Here’s what to consider before you upgrade—or decide to get an Apple Watch at all.

Car Crash Detection and Temperature Tracking

The new SE looks like the original SE, released in 2020, but has a processor that’s 20% faster. And it can now detect severe car crashes and alert emergency services and loved ones. The Series 8 looks like last year’s Series 7 but has crash detection, as well as new temperature sensors for menstrual cycle tracking.

Apple says car crash detection, which also comes in the new iPhone 14 lineup, uses a more sensitive accelerometer. Google has offered the same feature in its Pixel phones for years. The location-tracking app Life360, available on iOS and Android, can also detect some accidents.

Apple’s version won’t be triggered by fender benders, the company says; only severe collisions will automatically prompt the emergency feature. If the algorithm detects a crash, you’ll see a slider to call emergency services and notify emergency contacts. There’s also a 10-second countdown to dismiss the feature before the watch will activate its SOS function automatically, in case you’re incapacitated. You can also disable it.

My colleague Joanna Stern and I haven’t had a chance to safely test this yet. It’s an edge-case feature that I hope neither of us—nor you—unintentionally test.

On the Series 8, the temperature sensing doesn’t provide a thermometerlike instant reading. Instead, you’ll see changes from your baseline temperature in the Health app. You have to wear the watch for five nights while you sleep for it to begin gathering the data.

The sensor’s primary function is for tracking ovulation. The Cycle Tracking tool in Apple’s Health app already uses self-reported data to predict a user’s next menstrual period, and six-day fertile window, which represents the days leading up to, and including, ovulation. With the added temperature data, the app can now estimate what date ovulation occurred during the previous cycle. (Your temperature isn’t used for the predictive feature.)

It’s potentially useful data if you are trying to get pregnant or understand your cycle, but you have to know how to interpret it. Apple says its app shouldn’t be used as a form of birth control.

You can’t port the temperature data to other apps, such as Natural Cycles ($100 annually), which is FDA-cleared for birth control and offers ovulation prediction. Many fitness trackers, including the Oura ring and Fitbit, have similar temperature sensors and period-tracking tools.

However, among popular wearables, Apple’s Health app is the only cycle tracker to offer end-to-end encryption—which means Apple can’t view or share the data. The Supreme Court’s ruling striking down the constitutional right to an abortion brought more attention to popular services for tracking menstruation and ovulation, and how the health data held by these apps could be used against people in states where abortion may be criminalized.

I didn’t have a chance to collect a complete cycle’s worth of data to fully test the new Apple Watch feature; I hope to revisit the topic soon in greater depth.

Low Power Mode and Other WatchOS 9 Upgrades

Some of the Apple Watch’s best new features don’t require Series 8 or the updated SE. WatchOS 9, available as a free software update to Series 4 or newer models (including the original SE), comes with a medication reminder, sleep stage information, a feature to retrace your steps if you get lost on a hike, heart-rate zone training and my favorite: a low power mode that can extend battery life for up to 36 hours.

With the exception of the new Ultra, every Apple Watch since 2015 has been rated for the same 18-hour battery life. Finally, there’s a low power mode, like the iPhone’s, that shuts off nonessential features and extends the watch’s battery life to up to 36 hours. It cuts the always-on display and background heart-rate measurements while keeping activity tracking and fall detection—ideal for long flights or a weekend away without a charger. (For the new models, car crash detection and temperature sensing are also still enabled in low power mode.)

In my tests, low power mode extended the battery life of the Series 8—as well as my older Series 7 watch. The watches even had some battery left after 36 hours, but needed to be topped up to 30% for a second night of sleep tracking. (Apple’s 36-hour estimate is based on testing that doesn’t include sleep tracking, though sleep tracking still works when the feature is enabled.)

Which Watch Is Best for You?

All current Apple Watches offer GPS for recording outdoor activities, water-resistance for swimming, fall detection and heart-rate monitoring. You can listen to downloaded podcasts or Apple Music and Spotify playlists, as well as use credit cards with Apple Pay, all without an iPhone or cellular connection.

If the watch is for kids or senior loved ones who don’t own an iPhone, you’ll need to get a cellular model and use Apple’s Family Setup feature. (Most carriers charge extra to add a smartwatch to a cell plan.) Before signing up, know what the limits of cellular are: You can hail an Uber or send texts when you’re away from your phone—but you can’t send messages from third-party apps such as WhatsApp.

So, which watch is best? It depends. If you have a Series 4 or newer, start by upgrading to WatchOS 9. If you’re ready to spend, just remember: The more you pay, the more sensors you get.

SE ($249 and up): If you want the basic activity tracking and safety features, get the SE. There’s no always-on display, temperature sensor, blood-oxygen sensor or ECG app. Like the Series 8, it’s water-resistant down to 50 meters.

Series 8 ($399 and up): This model has a larger screen that stretches across more of the face and slightly larger case size than the SE, so it’s better for those who prefer large text. It’s also what to get if you want the more advanced health sensors and an always-on display. In addition to water resistance, the Series 8 is also dust resistant.

Ultra ($799): This model, available Sept. 23, has the biggest battery, rated for 36 hours—and up to 60 hours with a low power setting coming later this fall. It also has the brightest screen, and more advanced navigational capabilities. The Ultra can endure extreme temperatures and go down 100 meters underwater, twice the depth rating of the SE or Series 8. It’s aimed at long-distance athletes, outdoor enthusiasts and other active people who don’t like having to charge daily. We’ll see how it measures up in my review.

If you want more health data, but aren’t interested in crash detection or temperature tracking, check out last year’s Series 7. Retailers are offering discounts on it, and Apple is selling refurbished models for up to $100 off.