If you track your sleep with a smartwatch, you need to find a time to charge it that isn't the night.
Apple rates the Apple Watch Series 10 at up to 18 hours of normal use. Samsung rates the Galaxy Watch 7 (44 mm) at up to 40 hours with the always-on display off. So you charge it overnight, which is exactly when sleep tracking happens, or you find a daytime charging window. Any night it spends on the charger is a night with no sleep data.
The good news: you do not need a watch to track sleep. Devices without screens can track it too. This guide covers the real options, what each does well, and what to look for in the data once you have it.
What a smartwatch means for sleep tracking
Smartwatches are built to be glanced at. That affects sleep tracking in three ways.
The battery problem. A screen uses power, so a smartwatch needs charging more often than a screen-free device. If you charge at night, every night the watch sits on a charger is a night of missing data, and sleep metrics like your HRV baseline are more useful when the data is continuous.
The light and buzz problem. A screen and notifications can light up or buzz during the night. You can turn most of this off in the settings.
The comfort problem. Some people find a watch uncomfortable in bed and take it off to sleep. A tracker you remove at bedtime can't track your sleep.
None of this means smartwatch sleep data is useless. If you already own one, charge it in the morning while you shower and you will get your sleep data. If you are buying a device specifically to understand your sleep, compare battery life and how comfortable it is in bed.
What sleep tracking should actually measure
Before comparing devices, it helps to know what the data is. A good sleep tracker measures:
- Sleep stages. Time spent in light, deep, and REM sleep. Each stage does a different job, from physical repair in deep sleep to memory consolidation in REM. Our guide to sleep stages covers what each one means.
- Overnight HRV and resting heart rate. These two signals are the backbone of recovery tracking. More on this in our HRV tracking guide.
- Consistency. When you fall asleep and wake up, night after night.
- A summary score. A single number that rolls the night into something you can act on. Here is how sleep scores work.
Wearables estimate these from signals such as heart rate and movement, not in a sleep lab, so use them to watch trends. We looked at the research in our piece on sleep tracking wearables and their accuracy.
Option 1: A screen-free band
A screen-free band is a wearable stripped down to its actual job: sensors, a battery, and no display. All the data lives in the phone app, which you check when you choose to.
Because there is no screen to power, the battery lasts weeks instead of hours. The Penng band runs about 21 days on a charge, so you don't need to take it off to charge at night. No light, no notifications, nothing to charge before bed. It tracks sleep stages, overnight HRV, resting heart rate, and blood oxygen, and folds the night into a sleep score and a morning recovery score.
The trade-off is honest and obvious: no screen means no time check on your wrist and no mid-workout stats. If you want a device that does messages and maps, this category is not for you. If you want sleep data without charging every night, it is worth a look. We wrote more about who screen-free trackers suit.
Best for: people who want sleep plus full recovery and training data in one device, without babysitting a battery.
Option 2: A smart ring
Smart rings like the Oura ring take the same screen-free idea and shrink it onto your finger. Oura is built around sleep, and a ring is light: Oura says the Ring 5 weighs from 2g, depending on size.
The trade-offs: Oura gives the Ring 5 a battery life of 6 to 9 days, the ring starts at US$399 on Oura's own store plus a membership for most features, and Oura recommends its sizing kit before you choose a size. In South Africa, Oura sells through retailers and names Vitality as its authorised reseller, so check the local price there. We compared the two approaches in detail in Oura Ring vs Penng.
Best for: people whose single priority is sleep depth and who do not want anything on their wrist, ever.
Option 3: Bedside and under-mattress sensors
Nothing on your body at all. Under-mattress sensor strips and bedside radar devices estimate sleep from movement, breathing rate, and heart rate transmitted through the mattress or detected across the room.
The appeal is zero wearing friction. The limits are real, though. These devices only know about you in bed, so there is no daytime context: no workout strain, no resting heart rate trend during the day, no recovery picture.
Best for: people who refuse to wear anything and want basic sleep duration and consistency data.
Option 4: Your phone
Free sleep apps use the phone's microphone and accelerometer from your nightstand or mattress to estimate sleep. As a starting point, they beat nothing. They will show you roughly when you slept and flag loud snoring.
But a phone on your nightstand cannot read your heart rate, so there is no HRV or resting heart rate. There is also something self-defeating about ending a wind-down routine by putting your phone in your bed. Treat phone apps as a free trial of the habit, not the destination.
Best for: testing whether you care about sleep data before spending money.
How to choose
Ask two questions.
Do you want daytime data too? Sleep is half the recovery picture. If you train, your overnight numbers are more useful when you can see them next to yesterday's load. A screen-free band or a ring gives you the full loop. A mattress sensor or phone app only gives you the night.
How much friction will you actually tolerate? Be honest. If a device needs charging every few days, will you keep it alive for months? The longer the battery, the fewer charging gaps in your data.
For most people who want serious sleep data without a watch, the choice lands between a ring and a screen-free band. Sleep-only focus: ring. Sleep plus recovery, strain, and training in one app: band.
Using the data once you have it
A few rules that save people months of confusion:
- Trends beat nights. One bad score means nothing. Two weeks of declining deep sleep means something. Give any tracker a few weeks to learn your baseline before reacting.
- Act on the morning number. The whole point of sleep data is to shape today: training intensity, caffeine timing, an earlier night. A score you read and ignore is trivia.
- Start with the basics. Consistent bedtimes, a dark cool room and no late alcohol are good places to start. Our sleep hygiene checklist and guide to improving deep sleep cover more.
Frequently Asked Questions
Can I track my sleep without wearing anything?
Yes. Under-mattress sensors and bedside radar devices estimate sleep from breathing and movement, and phone apps offer a free option. Check which signals a device measures: a phone on your nightstand cannot read your heart rate, so it gives you no HRV or resting heart rate.
Should I use a screen-free band or a smartwatch for sleep?
It depends on how you want to charge and wear it. A multi-week battery means you don't need to take the band off to charge it at night, and there is no screen to light up or buzz while you sleep. A smartwatch suits you if you also want notifications, apps and GPS maps on your wrist, and you charge it at another time of day.
How do rings and bands track sleep?
Rings and bands read heart rate, HRV and movement from your skin, and they estimate sleep stages from those signals. Because they need charging less often than most smartwatches, you can usually leave them on overnight, which means fewer gaps in your data.
Do I need a subscription to track sleep?
It depends on the device. Oura needs a membership (US$5.99/month or US$69.99/year in the US) for most features, on top of the ring price. The Penng band costs R499 plus R49 shipping, which includes the band and 3 months of membership. After that it is R89/month or R890/year, paid in the Penng app. Many phone sleep apps are free, but they measure fewer signals.
Want to know if your sleep is helping or hurting your recovery? Take the free quiz at penng.ai/quiz, or see how the Penng band compares to watches and rings at penng.ai/compare.