Your watch already measured the night. KnowSleep does the other half — it lines that night up against what you actually did yesterday, and tells you the reason.
Coming soon to the App StoreiPhone + Apple Watch · No account · Nothing leaves your device
The problem
48 minutes of deep sleep, 58 bpm, HRV 42 — your watch has had those numbers all along. Reading them a hundred times still won't tell you what to change. What's missing is the sentence: "because you were still drinking coffee at three yesterday afternoon."
Working that sentence out needs one thing a watch cannot measure: what you actually did. That is the only thing KnowSleep asks you for.
How it works
How late your last coffee was, whether you moved, whether you drank, whether you were on your phone in bed. Four main tags, two taps. Workouts and caffeine can prefill from Health.
One page on last night: how long you slept, how the four stages fell, how far each sits from your own usual. Not a dashboard — something you can actually finish reading.
A tag needs several nights before KnowSleep will call it. Until then it says plainly "still counting, two more nights" instead of dressing up three days of data as a finding.
The point
Not "your sleep quality is below average" — anyone can say that. A sentence with your own numbers in it, and something you can go and change.
After enough nights
Which behaviours genuinely move your sleep, which ones don't, and which still need a few more nights — kept in three separate groups. "Not enough data yet" is never quietly rendered as "no effect".
Trends
No population ranking, no "you beat 68% of users". A single night bouncing around is normal; what matters is where your own line is heading.
Deep sleep, time to fall asleep, heart rate and HRV — over seven nights, thirty, ninety, or half a year as you drag.
Privacy
KnowSleep has no server. Not "we promise not to misuse your data" — there is nowhere for it to go.
No sign-up, no email, no phone number. Install it and it works.
Every calculation happens on this iPhone. No sync, no cloud backup.
Reads sleep, heart rate, HRV, blood oxygen, respiration, wrist temperature, workouts and caffeine from Apple Health. Writes nothing back.
No ad SDKs, no analytics SDKs. Delete the app and the data goes with it — we hold no copy.
Price
The brief is free. Paying is for the "why" and the full set of switches, and the paywall appears on the day your first real attribution is actually calculated — not before.
The 7-day trial does not start on the day you install — it starts once you have enough data for a first attribution. Prices are set in Chinese yuan; the App Store shows the matching local price in your region.