If you already wear an Apple Watch, most of what you need is already on your wrist. Sleep stages, a nightly sleep score, overnight vitals, a cardio fitness estimate and a training load view are built in, with no extra fee. What a separate app can add is mostly interpretation: putting the pieces side by side, comparing them with your own usual, and explaining what each number can and cannot tell you.
- 0.53Cohen's kappa for Apple Watch sleep stages against a sleep lab, best of six wrist devicesSchyvens et al. 2025
- 24 hbattery rating for Series 11, including six hours of sleep trackingApple
- 10 of 100points Aera's sleep score gives to sleep stagesAera
What Apple Watch already does on its own
- Sleep and sleep stages. With Track Sleep with Apple Watch turned on, the watch records time asleep and estimates time in REM, Core and Deep sleep, which you can review in the Health app on iPhone.
- Sleep Score. Since watchOS 26, the Sleep app gives each night a score out of 100: up to 50 points for duration, 30 for bedtime consistency compared with the previous 13 nights, and 20 for interruptions.
- Vitals. The Vitals app shows overnight heart rate, respiratory rate, blood oxygen, wrist temperature and sleep duration against your own typical range, which it builds over about seven nights of wear. Wrist temperature needs Series 8 or later or an Ultra; blood oxygen is not available on SE. On Series 12 and Ultra 4, heart rate variability (HRV) takes the place of sleep duration. Apple states that Vitals is not for medical use.
- Cardio fitness. The watch estimates VO₂max from how hard your heart works during outdoor walks, runs and hikes.
- Training load. Each workout gets an effort rating you can adjust, and the Activity app compares the intensity and duration of your last 7 days with the previous 28, from well below to well above.
All of this comes with the watch. You need a recent iPhone and current software, and some features depend on the model.
How a dedicated strap differs
WHOOP is the best known of the screen-free trackers. It is sold as a yearly membership in three tiers (One, Peak and Life) with the sensor included, and it tracks sleep, strain and recovery. WHOOP rates the battery of its 5.0 and MG sensors at about 14 days, and its battery pack can charge the sensor while you keep wearing it. The device has no screen, by design. Current prices are on whoop.com.
What each setup asks of you
A strap like this suits you better if:
- you want one device that stays on around the clock without a daily charge,
- you would rather have nothing with a screen or notifications on your wrist, or
- you find a watch uncomfortable in bed.
Apple rates the Series 11 at up to 24 hours of normal use, including six hours of sleep tracking, so wearing it every night means finding another time of day to charge. For many people a top-up during a shower or breakfast is enough.
How far to trust the wrist
Every wrist device estimates sleep from movement and heart rate. It does not record brain waves the way a sleep lab does. De Zambotti and colleagues (2019) reviewed wearable sleep technology and found these devices are generally good at telling sleep from wake and much weaker at separating the stages. Schyvens and colleagues (2025) tested six wrist devices against polysomnography in 62 adults; the Apple Watch Series 8 agreed best on sleep stages, with a Cohen's kappa of 0.53, which is moderate agreement, not a perfect match. So read time asleep and how broken the night was with more confidence than minutes of deep or REM sleep. More in watch sleep stages are an estimate.
A wrist tells sleep from wake well, and the stages much less well.
Heart signals need care too. Plews and colleagues (2013) argued for reading HRV as a rolling weekly average against your own baseline, because single mornings are noisy, and Buchheit (2014) made the same case for heart-rate measures in general: the trend against your own normal means more than any one value. See what HRV actually is and why a watch should compare you to yourself.
What an app on top can add
Several Apple Watch apps read Apple Health and build on it, each in its own way. What they tend to add:
- sleep, overnight heart signals and workouts on one screen instead of three apps,
- longer comparisons with your own usual, over weeks and months,
- a daily strain or load figure built from workout heart rate, and
- explanations of how each number is made and how much to trust it.
Before you pick one, check three things: whether it needs an account, where your health data is processed, and what is free versus paid. Many are free to start.
How Aera does this
Sleep in AeraLast night's score and time asleep, then the week as one line against your own sleep need, so a short night reads against what you usually need.
Aera, for iPhone and Apple Watch
Aera covers sleep and running, and every number in it opens a Field Guide article that shows how it was worked out and where it stops being reliable. There is no account, and your health numbers are worked out on your iPhone from what Apple Health already holds.
Its sleep score is weighted towards what a wrist measures well: time asleep against your own sleep need and how unbroken the night was count most, and sleep stages carry only 10 of 100 points because of the accuracy limits above. Workouts get a training strain figure from heart rate against your own usual, personal bests at every distance, and a route planner that keeps to real paths, with turn-by-turn directions on iPhone or Apple Watch.
Free: the daily scores, your sleep with its stages, workout summaries, personal bests, the route planner, a Flyover of any workout from the last seven days, the last 12 months of every trend, and your raw data as JSON or GPX. Premium is optional and adds the Sleep Reserve, history older than 12 months, reports, your places, more than one saved route, a written session for the day, and Flyover of older workouts. It is a subscription, monthly or yearly with a one-week free trial, or a one-time Lifetime purchase if you would rather not subscribe. The App Store shows the current price in your currency.
Aera is not a medical device. It needs a few weeks of your nights and workouts before its comparisons with your usual settle.
Quick answers
Can Apple Watch track sleep and training without a subscription?
Yes. Sleep stages, a nightly Sleep Score, overnight vitals, a cardio fitness estimate and training load are built into Apple Watch and the Health and Fitness apps on iPhone, with no extra fee. You only need the watch, a recent iPhone and current software.
Is Apple Watch a good Whoop alternative?
For many people, yes, especially if you already own one. It covers sleep, overnight heart signals and workout load. A dedicated strap suits you better if you want to wear one device around the clock for about two weeks between charges, or want nothing with a screen on your wrist.
How accurate is sleep tracking on Apple Watch?
Time asleep is the more dependable part. Sleep stages are estimated from movement and heart rate, not measured from the brain. In a 2025 lab study, Apple Watch staging agreed with polysomnography moderately well, the best of the six wrist devices tested, but far from perfectly.
What does an app on top of Apple Health add?
Mostly interpretation: putting sleep, heart signals and workouts side by side, comparing each with your own usual over weeks, and explaining how each number is made. Several apps do this, each in its own way, and many are free to start.
Related field notes: what a sleep score means · what VO₂max on a watch is · what training strain is · what a consumer watch cannot measure
Related guide: Should I run after a bad night's sleep?
Sources
- Apple Support. Track your sleep on Apple Watch and use Sleep on iPhone. https://support.apple.com/en-us/108906
- Apple Support. View your Sleep Score and sleep history on Apple Watch. https://support.apple.com/guide/watch/apded441a669
- Apple Support. Track your overnight vitals with Apple Watch. https://support.apple.com/120142
- Apple Support. Track your cardio fitness levels. https://support.apple.com/en-us/108790
- Apple Support. Track your training load on Apple Watch. https://support.apple.com/guide/watch/apde4c07a6cf
- Apple. Apple Watch Series 11, battery life. https://www.apple.com/apple-watch-series-11/
- WHOOP. Membership options. https://www.whoop.com/us/en/membership/ and WHOOP battery life. https://www.whoop.com/us/en/thelocker/how-long-does-whoop-battery-last/
- Schyvens D, et al. A performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnography. Sleep Advances. 2025;6(2):zpaf021.
- de Zambotti M, Cellini N, Goldstone A, Colrain IM, Baker FC. Wearable sleep technology in clinical and research settings. Medicine and Science in Sports and Exercise. 2019;51(7):1538-1557.
- Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Medicine. 2013;43(9):773-781.
- Buchheit M. Monitoring training status with HR measures: do all roads lead to Rome? Frontiers in Physiology. 2014;5:73.