A marker over
your stack.
Bitcoin-only widgets and a dashboard that keeps watch over your cold storage. Watch-only by design. Free, and collects nothing by default.
Developer-signed, verified on install. 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, network, and the Cycle Lab, read live from the same sources the app uses. 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 shitcoins or ask for your keys. Cairn does neither, on purpose.
Bitcoin only
No shitcoins, ever.
No accounts, no KYC
No backend that knows your name. Your wallets stay on your device.
Watch-only
Nothing in the app can move a single sat.
Point at your own node
Mempool, Esplora, BRK — all overridable. If mempool.space vanished tomorrow, Cairn wouldn't notice.
Your cold storage, watched.
Add an xpub, an output descriptor, a single address, or a Lightning wallet over NWC. Cairn tells you the moment it moves — especially when you didn't move it.
Watch anything
An xpub or descriptor, a single public address, or a Lightning wallet via NWC. Whatever you want an eye on, in one list.
Hidden, if you want
Tell a wallet never to show its balance — not in the app, not on the widget. Watching and alerts carry on; the number stays yours.
The moment it moves
Alerts on any change, up or down. There's also a spend alert that fires the instant an outgoing transaction hits the mempool, before it confirms. An unexpected spend is worth checking on.
On your phone, in your inbox
A notification with sound, an email, or both. Email is off unless you turn it on, and sends a bare "a wallet changed" note — nothing more.
Your keys stay put — the xpub, descriptor, or NWC secret you add is encrypted on the device with the Android Keystore and never leaves it. There's no account, and no Cairn server holding your wallets. To show a balance, Cairn looks your addresses up with a block explorer: mempool.space by default, or your own node if you point it there — so that explorer sees the addresses you watch, the same as any explorer would. Turn email alerts on and the only thing Cairn itself sends is the email address you verify and a bare "a wallet changed" note: never which wallet, the amount, or the bitcoin 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. 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 is the version where you don't have to open a terminal.
Or sideload it directly.
The same APK Zapstore serves, straight from this site. Android will ask for permission once — normal for a beta. 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 printed further down.
Allow the install
Android will ask whether to allow installs from this source. Say yes, just this once.
Open Cairn
Install, pin your first widget. The cairn is just stones until you start.
Don't take our word for any of it. The full 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.
v0.9.14 · beta · 8.0 MB · Android 8.0+
Free. No ads, no analytics, no KYC.