Android · early access beta
A marker over
your stack.
Bitcoin widgets for your homescreen, a dashboard for the full picture, and a watch on your cold storage. Cairn only watches: it never holds a key and never signs a transaction. Free, with no account and no analytics.
Signed by the developer, with the same key every release. 8.0 MB · Android 8.0+
Not on the Play Store yet.
Bitcoin, right now.
connecting…A glance at what Cairn puts on your homescreen: price, fees, blocks and the Cycle Lab, read live as this page loads. Read-only, like everything here.
Updated —. On-chain metrics are daily-close. Not financial advice.
What Cairn refuses to do.
Most Bitcoin apps on Android pad the ticker with other coins or ask for your keys. Cairn does neither, on purpose.
Bitcoin only
No altcoins, and no setting to add one.
No accounts, no KYC
Nothing to sign up for. No ads, no analytics, no crash reporting. Your wallets stay on your phone, encrypted.
Watch-only
It never holds a key and refuses private keys. Nothing in the app can move a single sat.
Point at your own node
Mempool, Esplora and BRK are all overridable, with a connection test before you save. Send everything through Tor with Orbot; if Tor drops, Cairn stops rather than going round it.
Your cold storage, watched.
Add an xpub, a single-sig output descriptor or a single address, or a Lightning wallet over Nostr Wallet Connect. Cairn tracks the balance and the cost basis, and tells you when it moves, especially when you didn't move it.
On-chain and Lightning, in one list
An xpub, ypub or zpub, a single-sig descriptor or a single address, Taproot included. Lightning from Alby Hub, Coinos, Zeus, Phoenix and others: balance and transactions only, never an invoice.
Hidden, if you want
Hide a wallet's amount and it stays hidden, in the app and on the widget. Watching and alerts carry on. The only way back is to remove the wallet and add it again.
When it moves
Alerts on receives, spends and balance changes. Every wallet also has a spend tripwire: if coins leave cold storage, it raises a critical alert on the unconfirmed spend, without waiting for a confirmation.
On your phone, in your inbox
A notification, an email, or both. Quiet hours run 22:00 to 07:00 by default, and only critical alerts make a sound in them. Email is off until you verify an address and switch it on for a wallet.
What leaves your phone. The xpub, descriptor or NWC secret you add is encrypted on the phone with the Android Keystore, never backed up to the cloud, and never sent to Cairn. To show a balance, Cairn looks your addresses up with a block explorer: mempool.space unless you set your own. That explorer sees the addresses you watch, as any explorer would; use Tor or your own node if you'd rather it didn't see your IP. Prices, news and cycle data come through cairn.wtf, and the request carries only your currency. Switch on email alerts and your email address goes to cairn.wtf so it can send them, with a note of which kind of wallet changed. Never which wallet, the amount or the address.
Get it from Zapstore.
Zapstore is an app store built on Nostr. Every release is signed by the developer's own key, and Zapstore checks that signature before anything installs. No store account, no gatekeeper in the middle.
Get Zapstore
Grab it from zapstore.dev. It's one sideload; after that it verifies everything you install through it, itself included.
Find Cairn
Search for Cairn and check the publisher. Every release is signed by one Nostr identity, ours, shown below.
Install, verified
Zapstore checks the APK signature against that identity before installing, and again on every update. A tampered build doesn't install.
Our Android signing certificate is publicly linked to that Nostr identity, so the direct download below carries the same proof. Zapstore just saves you opening a terminal.
Or sideload it directly.
The same APK Zapstore serves, straight from this site. Android asks for permission once, which is normal outside a store. If you skip Zapstore, do the checks below yourself.
Download the APK
The button below serves cairn-latest.apk. The SHA-256 to check it against is further down.
Allow the install
Android asks whether to allow installs from this source. Say yes, just this once.
Open Cairn
Install, then pin your first widget. The cairn is just stones until you start.
Don't take our word for any of it. The source is public: read it, rebuild it, and check what you downloaded. Three ways, strongest first.
A signed F-Droid build, verifiable independently, is planned for a later release.
Set your marker on the homescreen.
v0.9.15 · beta · 8.0 MB · Android 8.0+
Free. No ads, no analytics, no KYC.