Privacy Policy

Last updated 16 July 2026

This policy applies to the Cairn app (“the app”). Cairn is operated by Nilsen Lab (“we,” “us”). It’s short because Cairn is built to keep your data on your device. You can reach us any time at lukas@nilsenlab.com.

The short version

No accounts. No ads. No analytics or tracking. Your habits, history, and reminders live only on your device. The optional Companions feature shares a small anonymous daily summary, never your habit names, schedules, or history.

Data stored on your device

Your trails (habits), stacked stones (completions), history, streaks, reminders, and settings are saved locally on your device only. Local reminders are scheduled on the device and never leave it. You can export a JSON backup at any time and restore it later. The backup file is yours, and we never receive a copy.

Uninstalling the app or clearing its data permanently erases everything stored locally, so keep a backup if you are switching phones.

Companions (optional)

Cairn works fully offline. If you choose to turn on Companions, the app signs in anonymously with Firebase Authentication and stores a small amount of data in Google Cloud Firestore so you and your companions can see each other’s progress:

• The display name you choose (it can be anything, and defaults to “A wanderer”)
• Your six-letter trail code, used to connect with companions
• A random, anonymous identifier generated for your device
• A daily summary: the date, how many stones you stacked, how many trails you completed out of your total, and your longest streak
• Your companion connections and the pebbles (nudges) you send and receive, including any short note you choose to attach to a pebble

Your habit names, schedules, notes, and history never leave your device. The summary above is not tied to your name, email, or any real-world identity.

What we do not collect

• No names, emails, phone numbers, or accounts
• No location, contacts, photos, or files
• No analytics, advertising identifiers, or cross-app tracking

Deleting cloud data

You can delete everything Cairn has stored in the cloud at any time from the app’s Data & privacy screen. This removes your display name, trail code, summaries, companion links, and pebbles. Turning Companions off stops any further syncing.

Where data is processed

Companion data is processed by Google Firebase on our behalf. We do not share it with anyone else, and we do not sell data. There is nothing to sell.

Children

Cairn is suitable for all ages and does not knowingly collect personal information from anyone, including children. Companion data is anonymous.

Changes

If this policy changes, we’ll update the date at the top of this page.

Contact

Questions or requests? Email lukas@nilsenlab.com.