Privacy Policy

Effective date: 2026-04-20

Chronosync Plus is a local-first self-tracking app. Your data stays on your phone, encrypted with a key derived from your password. We do not run a server, we do not collect analytics, and we do not sell or share your information with advertisers.

1. Data stored on your device

All of the following are held in local, encrypted app storage on your phone. Nothing here leaves your device without your explicit action (e.g. tapping Export in Settings).

Email address (used only as a display label on the login screen).
Chronotype, skin type, clothing preset, blue-light settings.
Sleep and wake times you log.
Sun-exposure sessions and total vitamin-D IU for today and your 90-day history snapshot.
Morning-light minutes and peak lux.
Blocklist of distracting apps selected in Focus mode.
Glasses-worn state, streaks.

Encryption. On sign-up, a 256-bit AES-GCM key is derived from your password via PBKDF2-HMAC-SHA256 with 310,000 iterations and a random 16-byte salt. Every Zustand store snapshot on disk is encrypted with that key before being written. The key lives only in RAM while you're logged in and is wiped from memory when you lock the app or after 5 minutes of background time.

2. Data that leaves your device

Destination	What's sent	Why	When
`api.open-meteo.com`	Latitude + longitude	Current UV, cloud cover, and 24-hour hourly forecast	Every 15 min while the app is open with location set
`nominatim.openstreetmap.org`	Latitude + longitude	Reverse geocode to a place name	Only when you tap the location label or change location
`timeapi.io`	Latitude + longitude	Resolve IANA timezone for your location	Only when you change location or your device's timezone changes

No API keys, account identifiers, or user-identifying headers are sent. These third parties log inbound traffic according to their own privacy policies (linked below). We recommend reviewing them.

Open-Meteo: open-meteo.com/en/terms
OpenStreetMap Nominatim: osmfoundation.org/wiki/Privacy_Policy
timeapi.io: timeapi.io/privacy

3. Data we do NOT collect

No accounts on a Chronosync Plus server (there is no server).
No telemetry, analytics, or crash reports.
No advertising identifiers (Android Advertising ID, IDFA, Firebase IIDs).
No third-party SDKs that phone home.
No cookies.
No camera frames — the Lux Meter reads brightness from the live preview stream only. Frames are not recorded, saved, or transmitted.
No microphone access.
No contacts or calendar access.
No records of which apps you use. The Focus-mode blocker queries the current foreground app in-memory only and compares it to your blocklist. The observation is wiped from memory when you stop a focus session.

4. Permissions we request and why

Permission	Reason
Fine/Coarse Location	To compute solar times, UV, and the vitamin-D window for your position.
Camera	Lux Meter brightness estimation when no hardware ambient-light sensor is available. Only active while the meter screen is open.
System Alert Window	System-wide blue-light overlay. The overlay is marked NOT_TOUCHABLE and never captures taps or reads screen contents.
Package Usage Stats	Focus-mode app blocking. Used to detect which app is in the foreground; never logged or transmitted.
Post Notifications, Schedule Exact Alarm, Full-Screen Intent, Vibrate	Ringing solar alarms and glasses reminders, scheduled locally.

5. Children

Chronosync Plus is intended for adults 18+. It is not designed or marketed for children and should not be used by children under 13.

6. Not medical advice

Chronosync Plus is a self-tracking tool, not a medical device. Burn times, vitamin-D IU estimates, circadian phases, and coaching tips are outputs of general physiological models — not clinical measurements, not prescriptions. Do not use Chronosync Plus to decide whether to take, adjust, or stop any medication, supplement, or therapy. Always consult a qualified clinician.

7. Backup / transfer

Tapping Settings → Export produces a JSON file containing your encrypted Zustand snapshot plus auth record (salt + verifier). The file is safe to share: without the password, nobody can decrypt it. Importing the same file on another device restores your data if you enter the same password.

Android auto-backup is disabled for Chronosync Plus so the encrypted store is never silently uploaded to Google Drive.

8. Data retention

As long as the app is installed and the user is logged in: all data above.
On log-out: the session key is wiped from memory; the encrypted store remains on disk until the next login.
On "Reset all data" (Settings → Reset): every record is removed.
On uninstall: Android removes the entire app directory.
We retain nothing on a server, because there is no server.

9. Changes to this policy

This document is shipped in-app under Settings → Privacy Policy and mirrored at this URL. Material changes will trigger the in-app "What's new" panel on the next launch after an update.

10. Contact

Email: support@chronosyncplus.com