Sleep tracker for the watch you already wear
How wearables estimate sleep and stages from movement and heart rate, what they get right, and how FORM puts last night next to your food and training.
How do sleep trackers measure sleep?
Most sleep trackers estimate sleep from movement and heart rate. Long stillness suggests you’re asleep, and changes in heart rate and its variability help the algorithm guess the stage: light, deep or REM. A lab sleep study, called polysomnography, measures brain waves directly. A wearable can’t, so its stages are estimates, useful for trends across weeks and less reliable for any single night.
How it works in FORM
- Wear your watch or tracker to bedAny wearable that writes sleep to Apple Health or Health Connect works, including Apple Watch, Garmin, Oura, WHOOP and Fitbit.
- Connect Apple Health or Health ConnectGrant FORM access to sleep. FORM has no sleep sensor of its own, so this is where the night comes from.
- Open FORM in the morningLast night’s sleep and stages, deep, REM, light and awake, sit on today next to your meals and training.
- Read the week, not the nightLook at the pattern across several nights. One short night says less than a run of them.
A sleep tracker doesn’t watch you sleep. It watches your wrist or your finger and makes an educated guess. Knowing how that guess is made tells you which numbers to trust and which to read loosely.
How a wearable estimates sleep
Movement comes first. When your wrist goes still for a long stretch, the tracker assumes you’re asleep. Heart rate adds detail. It drops as you settle, and its rhythm shifts between stages. Some devices also use breathing rate, skin temperature or blood oxygen. The algorithm combines these into a guess at when you fell asleep, when you woke, and which stage you were in.
A lab sleep study is different. Polysomnography records brain waves, eye movement and muscle activity, and that’s how sleep stages are defined in the first place. A watch measures none of those. Its stages are a model of what your brain was probably doing. That’s still useful. It just isn’t the same thing. For what each stage does, read sleep stages, explained.
What to trust, and how much
| Measure | How the wearable gets it | How to read it |
|---|---|---|
| Total sleep time | Long stillness and a lower heart rate | Fairly reliable for trends. Can run high, because lying still awake looks like sleep. |
| Bedtime and wake time | When stillness starts and ends | Useful for checking how regular your schedule is |
| Time awake in the night | Movement and a rise in heart rate | Short wakes are easy to miss. Treat it as a rough count. |
| Deep, REM and light sleep | Heart rate patterns and movement, run through a model | Estimates. Useful across weeks, weak for a single night. |
| Night-to-night trend | All of the above, over time | The most useful thing most trackers give you |
What FORM does with your sleep
FORM has no sleep sensor and no Apple Watch app. It reads sleep and sleep stages from Apple Health on iPhone, or Health Connect on Android, using whatever your wearable wrote there. Apple Watch, Garmin, Oura, WHOOP, Fitbit and other wearables that sync to Apple Health or Health Connect all work.
Then it puts the night on the same day as your food and training. That’s the point. A sleep app shows you a chart of your night. FORM shows it next to the late dinner, the evening coffee, the two glasses of wine and the hard session that came before it. Patterns you’d never spot across three apps are easier to see on one screen. A tracked night also feeds your recovery score.
When sleep tracking works well, and when it struggles
- Works well: regular nights in your own bed, with the watch snug and charged.
- Works well: spotting patterns, like shorter sleep on nights you train late or drink.
- Struggles: lying awake very still. Many trackers count that as light sleep.
- Struggles: naps, broken nights with a baby, and shift work, which can confuse sleep algorithms.
- Struggles: a flat battery. No data means no night in FORM, and no recovery read that day.
Honest limits
A wearable is not a medical sleep test, and FORM does not diagnose sleep disorders. If you snore loudly, someone has noticed you stop breathing at night, or you wake up exhausted after a full night, talk to a doctor. A proper sleep study is what answers that. Don’t chase a stage number either. Worrying about last night’s deep sleep can keep you up tonight, which defeats the point.
How sleep connects to the rest of the day
Sleep is one of the five pillars on FORM’s Today dial, next to Food, Recovery, Activity and Training, and it feeds your daily Health Score. A short night can change the rest of the day too: more snacking, a slower session, a third coffee. Seeing the night next to the day makes that visible. If bedtime keeps drifting, set a wind-down reminder. For setup, see connecting Apple Watch and Apple Health. For the bigger picture, read how FORM tracks sleep, stress and recovery.
FAQ
Can FORM track sleep without a watch?
No. FORM has no sleep sensor. It needs a wearable, or another app, that writes sleep to Apple Health or Health Connect.
How accurate are Apple Watch sleep stages?
Like any wearable, Apple Watch estimates stages from movement and heart rate rather than brain waves. Treat them as estimates that are useful across weeks, not as a lab result.
How much sleep do adults need?
The American Academy of Sleep Medicine recommends seven or more hours a night for adults. Individual needs vary.
Why does my tracker say I slept when I was awake?
Trackers lean on movement. If you lie very still while awake, the watch can read it as light sleep.
Does FORM show deep and REM sleep?
Yes, if your wearable records stages. FORM reads deep, REM, light and awake from Apple Health or Health Connect.