Why Doesn't the Apple Watch Series 5 Track Sleep?

The Apple Watch Series 5, introduced this week, comes with a few new features, including an always-on Retina display, a built-in compass app, period tracking, and activity stats, but it still lacks one basic function: sleep tracking.

It's easy to see why Apple chose not to include sleep tracking on the Series 5. For starters, there's battery life. While the new smartwatch's low-temperature polysilicone and oxide display (LTPO) is meant to preserve power, Series 5 battery life is still 18 hours, the same as the Series 3 and 4. Design is also important to consider. The Series 5 is a sleek, premium wearable, but it doesn't look like the most comfortable device to wear to bed.

It's also clear that heart health features are the main focus here. At Tuesday's press event, Apple opened the Apple Watch section with a video montage of users sharing stories about how the ECG reader and heart rate monitor (on the now discontinued Series 4) alerted them or others to serious health conditions and helped save their lives.

But it's tough to label the Apple Watch as a well-rounded health and fitness wearable when it's no secret that sleep greatly impacts our overall wellbeing, especially cardiovascular health. According to the Center of Disease Control and Prevention, adults who get less than seven hours of sleep every night are more likely to have a heart attack, stroke, high blood pressure, type 2 diabetes, and obesity. While the Apple Watch can detect sleep apnea, it's important to take additional health issues into consideration as well.

Sleep is also the driving force behind performance. In a study done by researchers at the Department of Psychiatry and Behavioral Sciences at Standford University in 2009, students on the Stanford Women's tennis team had faster sprinting drills and increased hitting accuracy and depth following nights of extended sleep.

While the Apple Watch isn't strictly worn by athletes, sleep tracking could help users improve their workout performance on a daily basis. Even basic sleep metrics like duration or time spent awake could help users make more informed decisions about their health and fitness.

Of course, relying on an accelerometer, heart rate monitor, and microphone on your wrist to measure sleep quality leaves room for error. I've had mixed results when reviewing the feature myself. The Huawei Watch GT, for example, said I was in a light sleep stage when I was actually scrolling through my phone while sitting in bed. Meanwhile, the Withings Move ($149.95 at Amazon) confused stagnance for sleep when I left the watch on my desk for a couple of hours.

In our tests, devices from Fitbit—like the Versa—delivered mostly accurate results on what was actually measurable, including the time I went to bed and woke up, as well as sleep duration. But without the proper technology, like electoencephalogy (EEG sensor) to measure brain activity while asleep, it's tough to know whether or not it's accurately identifying sleep stages.

But at least Fitbit is making an effort to improve its sleep-tracking technology. Last month, it launched a Sleep Score app alongside the Versa 2 ($75.00 at Walmart) which uses the heart rate monitor and SPO2 sensor to track sleep duration, sleep stages (light, REM, and deep sleep), and restoration (your heart rate while asleep) to score your sleep quality between 1 to 100. While the app was in beta for almost a year, Fitbit collected anonymous data from over 10,000 users in order to help better understand the correlation between sleep quality, sleep disturbances, and signs of potential health problems.

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Apple, on the other hand, says it's collecting data on other features instead. During Tuesday's event, the company announced an Apple Hearing Study (used in conjunction with the watchOS 6 Noise feature), a Women's Health Study (used with the cycle-tracking feature), and the Apple Heart & Movement Study. While these areas of study are important when it comes to overall health, a sleep study should also be part of the mix—especially since the Apple Watch already packs the sensors needed to track basic sleep metrics, and the iPhone's Health app comes with a Sleep Analysis feature.

If you're still set on buying the Apple Watch Series 5, there are third-party apps that track sleep. But since they're not native to the device, the analytics don't factor in other metrics tracked by the watch. For a smartwatch that comes with a starting price of $399, it'd be ideal if it could paint a full picture of my overall health, sleep included, rather than just part of it.

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