Whatever you wear writes to Apple Health. IntentNorth reads it and changes what today asks of you: the session, the evening, the order things happen in. Nothing else you own does anything after the number.
- A short night changes today’s session, and the session says why. Under six hours and the hard lifts stay while the smaller exercises come out. The session carries the app’s own sentence — “Short night — main work stays, accessories rest today” — so you can disagree with it.
- Read against your own normal from the last fourteen days, never a population band you were never in. Healthy adults sit anywhere from about 20ms to 200ms of heart-rate variability, so an app that colours a number red against a population range is telling half its users something false.
- No new device, no second subscription, no account. IntentNorth does not sell hardware and does not need any. It adds no health subscription on top of whatever your device already charges.
What we read, and what we don’t
Seven things from Apple Health and nothing else. We never write to Health — the adapter is read-only by construction. We do not read your messages, your location, or your workouts blow by blow.
- How long you slept
- The one that changes the most. Under six hours and today's session keeps the hard lifts and drops the smaller exercises.
- Resting heart rate
- Compared against your own median from the last fourteen days. Five beats over is worth noticing; ten changes the session.
- Heart-rate variability
- Used the same way, when your device writes it to Apple Health. Many do not — see below.
- Cardio fitness (VO₂ max)
- Apple Watch and Withings supply this. Garmin deliberately withholds it. You can type it in.
- Body weight
- Read as a three-week trend, never as this morning's number.
- Height
- A profile field, typed once.
- Waist
- A tape measure and a text field. No wearable in the category writes this.
No wearable at all? Every one of those can be typed in, and sleep hours too. The plan works without a device; it just stops adapting to the nights.
The thing nobody tells you about HRV
Apple Health stores heart-rate variability as SDNN. Oura and Whoop both compute it as RMSSD, a different statistic, and neither writes HRV into Apple Health at all. So if you own one of those, we do not see your variability figure — and any app telling you it works with your Oura or Whoop HRV is describing something that does not happen.
It matters less than it sounds. Sleep and resting heart rate are close to universal across devices, and those two are what the short-night rule and the resting-heart-rate comparison actually run on. Variability makes the reading sharper where a device provides it; it is not the thing holding the system up.
Which devices, specifically
We will name the three families that were checked rather than say “any wearable”, because that is not true:
- Apple Watch. The only one that reliably fills all four of sleep, resting heart rate, variability and cardio fitness. Nothing extra to pay for the sync.
- Garmin, through Garmin Connect. Sleep with stages, resting heart rate, weight. Garmin does not pass on its cardio fitness figure. Connect+ is an extra tier and is not needed for the sync.
- Withings. The one non-Apple family found that sends cardio fitness as well as sleep, heart rate and weight, and the clean case for a connected scale.
Rings and bands from Oura, Whoop, Ultrahuman, RingConn, Fitbit, Polar, Coros and others write sleep and resting heart rate, which is enough for the parts that matter most. Suunto writes neither, so it will not drive anything.
We do not replace the app your band came with
It measures; we decide what the day does about it. Keep it, keep whatever it costs, and let it keep writing to Health. If you stop wearing the band the plan keeps working — it just stops adapting to the nights.
And we will not tell you to buy hardware and cancel the membership, which is the advice going round. For Whoop it is simply false: the company’s own cancellation page says that once cancelled you cannot collect, upload or analyse any of your data, so nothing reaches Apple Health and the band is a bracelet. For Oura, the Apple Health integration on current rings is listed as needing an active membership, so cancelling would break the exact connection we depend on.
This is a training input, not a health assessment
A low reading changes how many of the smaller exercises a session includes. It never says anything about whether you are unwell, and it must not start to. If a number worries you, that is a conversation with a doctor and not with an app.
See what a week looks like — or read the honest Whoop comparison, which names a cheaper app than ours if a daily readiness number is all you want.
Device behaviour recorded 7 September 2026 from vendor support pages and the Australian App Store. Vendors change what they sync; check yours if it matters to your decision. Education, never diagnosis or personal advice.