A native Android sync adapter that brings your Proton Contacts and Proton Calendar to every app on your phone — fully encrypted, fully offline-capable.
Proton offers no CalDAV/CardDAV, so the usual sync apps can’t reach it. Here’s how the realistic options line up.
| Capability | Sync Provider | DAVx5 / CalDAV apps | Proton’s built-in options |
|---|---|---|---|
| Proton Contacts on your phone | YesTwo-way | NoNothing to connect to* | Manual vCard export/import |
| Proton Calendar on your phone | YesTwo-way | NoNothing to connect to* | View-only share link, or .ics export/import |
| Edits on your phone sync back to Proton | Yes | No* | No |
| Keeps syncing automatically | YesOn your chosen interval | No* | View-only calendar share link at most |
| No server, relay or self-hosting | Yes | NoNeeds a CalDAV/CardDAV server* | Yes |
* DAVx5 is an excellent CalDAV/CardDAV client — but it needs a server that speaks those protocols, and Proton doesn’t provide one, so it can’t reach Proton. Full explanation: Proton, CalDAV/CardDAV & Android sync. (As of June 2026.)
Here’s exactly what lives where on your device, so you can decide if the trade-offs fit your threat model. Nothing on this list leaves your device except via Proton’s own API — there are no analytics, no crash reporters, and no third-party destinations.
AccountManager, with file-based encryption when the device is lockedContactsProvider, same place your Google and Samsung contacts liveCalendarProvider, same place your other calendars liveWhy plaintext at all? This is the whole point of a native sync adapter: once decrypted, your Proton contacts show the right name when someone calls you, and your Proton events appear on your watch, your lock screen, and in whatever calendar app you prefer. If the data stayed encrypted inside the app, none of that would work. The same security model applies to every sync adapter on Android — Google, Samsung, iCloud, DAVx5. The at-rest protection above guards against casual disk inspection, backups, and apps without the right permissions; it does not protect against a rooted device or a malicious app that already has READ_CONTACTS / READ_CALENDAR.
Want stricter isolation? If you’d rather have no data touching Android’s system providers — or any other link in the chain — stay with Proton’s official Android apps, which keep everything in-app. You give up system-wide integration in exchange for zero additional trust.
Every feature, free for 7 days — no commitment, cancel anytime.
or €23.99 / year · incl. German VAT (other countries may differ)
Features and pricing are indicative and subject to change until final release. Payments processed by Paddle.com (direct channel) or Google Play (Play channel).
Same app, same price. Pick the channel that fits your device — only the way you start the trial and pay differs.
Install and subscribe straight from the Play Store. Your 7-day free trial and billing are handled entirely by Google Play.
No Google account needed. Install via Obtainium or sideload the APK, then purchase a license on the web and activate it with your subscription ID — same 7-day free trial.
The Play and direct builds are signed with different keys, so switching between them needs a reinstall.
Not for syncing. Proton doesn’t offer a CalDAV or CardDAV endpoint, so standard clients like Apple Calendar/Contacts, Thunderbird or DAVx5 can’t sync Proton Calendar or Proton Contacts over those protocols. Proton does let you share a calendar via a view-only link and export/import .ics files, and Proton Contacts can export/import vCard — but that’s read-only or a one-off snapshot, not live two-way sync. (As of June 2026.)
DAVx5 is a CalDAV/CardDAV client — it connects to a server that speaks those protocols. Proton doesn’t provide one, so there’s nothing for DAVx5 to point at, and Proton isn’t among DAVx5’s tested providers. Sync Provider takes a different route: it talks to Proton’s own API and writes contacts and events straight into Android’s system Contacts and Calendar. There’s a fuller explanation here.
Sync Provider writes your Proton contacts into Android’s system Contacts provider and your Proton events into Android’s Calendar provider — the same places Google and Samsung keep theirs. So your Proton contacts appear in Samsung Contacts, Google Contacts and your dialer, and your Proton calendar shows up in Google Calendar and other calendar apps, on your lock screen and on your watch.
Yes. It uses Android’s built-in sync framework rather than Google Play Services, so no Google account is required. On standard Android you can install from Google Play; on GrapheneOS or other de-Googled devices, install via Obtainium or the GitHub releases and activate a licence on the web.
No. Sync Provider syncs directly between Proton’s API and your phone. There’s no Nextcloud instance, no self-hosted bridge, and nothing to keep running.
Yes to both. Edits on your phone sync back to Proton and vice-versa, and all contact and calendar data is end-to-end encrypted with OpenPGP using your own Proton keys — your password never leaves your device (SRP). The Data & Encryption section above shows exactly what is stored and where.
Replies are personal — no ticketing systems, no chatbots.
Please include your Android version, device model, and the app version (Settings → About) when reporting bugs.
A Firefox & Chrome extension to read, compose, and manage Proton Mail right from the browser toolbar — without ever opening a tab.