Turn a spare phone into an air-gapped Bitcoin signer.

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$0
FREE
Free, forever. No upsell. No paid tier. No business model that needs you to keep paying.
0
ACCOUNTS
No email. No signup. No phone number. Nothing for anyone to leak about you.
0
TELEMETRY
Nothing about you leaves the device. Ever. The app has no way to phone home.
// SECTOR / 01 - protocol

Three steps.
Then forever.

One install. One factory reset. Then never again.

1

Take any spare phone

iPhone or Android, six years old or newer. Factory reset. SIM out. Airplane mode on. That phone is done with the network.

2

Install hypergap

Generate or import a seed. The phone’s secure element seals it with a key that cannot leave the chip. The seed only exists in plaintext for the moment it takes to sign - pull the battery and even that moment is gone.

3

Sign through the camera

Your online wallet shows an unsigned transaction as a QR code. Hypergap reads it through the camera, decodes it on the offline phone, and shows you the details - address, amount, fee - to confirm with your own eyes. Then it signs and shows the signature back as a QR. The keys never leave the offline phone.

// SECTOR / 02 - capabilities

What Hypergap does.
And why the phone never reconnects.

Every feature you would expect from a hardware wallet, and several you would not. All offline. All open source. All running on a phone you already have.

PSBT

Air-gapped PSBT signing

Full PSBTv2 support over animated UR/UR2 QR with Luby Transform fountain codes. Pairs with Sparrow, Specter, Electrum, BlueWallet, Nunchuk, Caravan - anything that speaks PSBT over QR. Private keys never touch a wire.

Multisig

Bitcoin multisig, end to end

Coordinator and cosigner roles. P2WSH, P2SH, P2TR script-path, BIP-48 descriptors. 2-of-3, 3-of-5, and geographically distributed setups without a $500 hardware bundle.

Taproot

Taproot - key-path and script-path

Schnorr key-path signing for single-sig and MuSig2. Script-path for Taproot policies. BIP-340 nonces derived deterministically inside the secure element.

BIP-85

Deterministic child seeds

BIP-85 derivation generates unlimited child wallets from one master seed. Decoy wallets, family wallets, time-locked wallets - all from a single paper backup.

BIP-322

BIP-322 message signatures

Prove ownership of an address without spending. Used by exchanges, lending platforms, and proof-of-reserves audits. Signed inside the secure element, displayed back as QR.

Entropy

Verifiable entropy

Roll dice. Flip coins. Mix sensor noise from camera, microphone, accelerometer, and gyroscope. SHA3-256 accumulator. Verify every bit of randomness that creates your seed.

4 schemes

Four backup schemes

Shamir Secret Sharing, SSKR (Blockchain Commons), Seed XOR (Coldcard-compatible), and Hamming 2-of-3. Mix and match by threat model. Every share is a valid BIP-39 mnemonic.

Duress

Eight duress PINs

Wipe & reboot, silent wipe, decoy wallet, brick device, countdown, look-blank, delta mode, reboot-and-wipe. Inspired by Coldcard Trick PINs - your seed survives the wrench.

// SECTOR / 03 - interface

One app.
Three jobs. Nothing else.

Hold keys. Confirm transactions. Scan what to sign. The app does not do anything else, because anything else is attack surface.

9:41✈

Hypergap

▸ AIR-GAPPED · 14d 02h
Cold storage
8a4f · 9bc1 · 207e
BTC
Lightning hot
3d92 · 1f8b · 6e44
LN
Family multisig
b720 · 0c4a · 9f3d
BTC
9:42✈
▸ confirm signature
₿ 0.5000
≈ $34,210 USD
From bc1q…8nqv
To bc1q…4xv7
Fee 0.0001
Chain Bitcoin
Key Cold storage
Hold to sign · 3s
9:43✈
▸ scan to sign
FRAGMENT 7 OF 11
RX 65% · CRC OK
▸ HOME · SIGN · SCAN - same offline app on iOS and Android.
// SECTOR / 04 - architecture

Layered defense,
around your seed.

From the network boundary to the silicon. Each layer operates independently - compromise one, the others hold. Click any ring for the full explanation.

01 No network data plane.

Permanent air-gap

No networking. The only networking code is a detector which marks the device as compromised if it succeeds. It is not used for sync, telemetry, remote config, update checks, backups, crash reports, or wallet-data transport. Combined with a phone in airplane mode and the SIM ejected, any successful network path becomes an alarm, not a feature.

// SECTOR / 05 - threat model

Built for adversarial conditions.

FTX, Celsius, BlockFi. Tornado Cash sanctions. Border seizures. The wrench attack. Hypergap assumes the worst threat model and designs the device for it.

Coercion

The $5 wrench attack

Eight duress PINs. Wipe and reboot. Silent wipe. Open a BIP-85 decoy wallet with small funds. Brick the device permanently. Show a countdown. Look freshly installed. Allow spending but block seed viewing. Each PIN, a different defense. Under coercion, you choose which one fires.

Border crossings

Hostile inspection

A factory-reset-looking phone with no apps, no accounts, no SIM card, and a benign decoy wallet behind a separate PIN. Plausible deniability built into the architecture, not bolted on as a feature flag. Keys derive from a seed only you remember - and never appear on screen unless you ask.

Surveillance

Permanent air-gap

No SIM, no Wi-Fi, no network data plane. The only networking code is a detector which marks the device as compromised if it succeeds. There is no sync, telemetry, remote config, backup, crash report, or wallet-data upload to capture.

Counterparty risk

Post-FTX self-custody

No accounts. No KYC. No servers we run. The seed is generated on-device, stored in the secure element, and never leaves it. If we disappear tomorrow, your keys are unaffected and your funds keep moving on the next compatible wallet you install.

// SECTOR / 06 - deploy

Six steps.
Thirty minutes. Then it's done.

Setting up the dedicated air-gapped phone. The device is online exactly once - long enough to install Hypergap - then never again.

  1. 01

    Pick a spare phone

    Any iPhone with Secure Enclave (6s+) or Android with StrongBox (Pixel 3+, recent Samsung flagships). Older is fine - fewer concerns about resale value, same hardware key isolation.

  2. 02

    Factory reset

    Erase everything. Set up as a brand new device. Skip iCloud / Google account, biometrics-tied-to-account, location services, and Siri or Assistant. The phone has no identity other than "Hypergap signer".

  3. 03

    Install Hypergap

    Connect to a trusted network exactly once. Install from the App Store or Play Store, or sideload a reproducibly-built APK / IPA after verifying its hash. Then install nothing else.

  4. 04

    Sign out and lock down

    Sign out of any Apple ID or Google account. Disable iCloud Keychain, Find My, automatic backups, and auto-updates. Set a long PIN. Disable biometric unlock if your threat model requires it.

  5. 05

    Air-gap the device

    Eject the SIM. Disable Wi-Fi, Bluetooth, NFC, AirDrop, and cellular data. Enable airplane mode and leave it on. Optional: keep the device in a Faraday pouch when not in use.

  6. 06

    Generate the seed offline

    Open Hypergap. Generate a seed using verifiable dice or coin entropy. Back up to one or more of the four schemes: Shamir, SSKR, Seed XOR, Hamming. Distribute shares geographically.

// SECTOR / 07 - principles

Three rules.
Never bent.

RULE / 01

A signer you already own

Any iPhone or Android from the last six years. No specialty device to order, no customs to clear, no new supply chain to trust beyond the one your phone is already on.

RULE / 02

An air gap, in the literal sense

Every byte in, every byte out, travels through a QR code on a screen. The camera reads. The screen writes. One direction at a time. No bluetooth, no USB, no wireless pairing - the only channel between the offline phone and the world is one you can watch happen.

RULE / 03

Open all the way down

Every line of code is public. Releases are reproducibly built. You can verify the binary on your phone matches the source on GitHub - yourself, by hand, no trust required.

▸ designed to pair with SparrowSpecterZeusNunchukBluewalletBitcoin Keeper
// SECTOR / 08 - ecosystem

Pairs with the wallets
you already trust.

Hypergap is the offline half. Your favorite Bitcoin wallet keeps being the online half - same UI you know, same flows, plus a camera and a QR.

Sparrow
PSBT coordinator
Specter Desktop
Multisig HQ
Electrum
Veteran client
BlueWallet
Mobile online half
Nunchuk
Multisig & collab
Zeus
Lightning watch-only
Bitcoin Keeper
Inheritance flows
Caravan
Browser multisig

Your keys never leave.
Your phone never connects.
Your secrets never ride.

- HYPERGAP
// SECTOR / 09 - vs hardware

Hypergap vs
Ledger, Trezor, Coldcard, SeedSigner, Keystone.

A dedicated phone with Hypergap matches dedicated hardware on every column that matters - and wins the ones nobody else competes on.

HypergapLedgerTrezorColdcardSeedSignerKeystone
Price Free $79–$399 $69–$219 $160+ BYO hardware $129–$169
Hardware to buy None Yes Yes Yes RPi + screen Yes
Supply-chain trust required None Reseller chain Reseller chain Direct only Self-source Reseller chain
Air-gapped by default USB / BT USB
Verification screen Full-size phone 128×64 mono Color, small 128×64 mono 1.5" mono 4" color
Bitcoin multisig Coord + cosigner
BIP-85 child seeds
Backup schemes 4 (Shamir+SSKR+XOR+Hamming) Shamir Shamir Seed XOR SeedQR / BIP-39 Shamir
Duress / decoy modes 8 modes Passphrase only Trick PINs Passphrase only Passphrase only
Verifiable entropy (dice/coin) Dice + coins + sensors Dice Dice / coin
Open source Partial Partial
Reproducible builds Target v1
Hides in plain sight Just a phone Obvious Obvious Obvious DIY box Obvious
// SECTOR / 10 - services

Free signer.
Optional services.

Everything that runs on the dedicated phone is free, forever. No subscriptions, no accounts, no security feature ever gated behind a paywall. The optional services below add convenience - never custody, never gating.

Hosted

Hypergap Backup

End-to-end encrypted cloud backup for everything that is not a seed - descriptors, labels, recovery instructions, signer policy. Encrypted on the offline phone before it ever leaves; we host opaque bytes. Free tier; sat-priced unlock for unlimited vaults and cross-device restore.

Learn more →
Hosted

Hypergap Coordinator

Hosted multisig coordinator. Stores public descriptors, relays PSBTs between cosigners, never sees a private key and never has custody. Free tier; sat-priced unlock for unlimited vaults and offline backup of the coordinator state.

Learn more →
Annual

Hypergap Inheritance

Dead-man's switch. After a configurable inactivity period, encrypted instructions are released to heirs you designated. End-to-end encrypted on your device; we cannot read instructions and cannot hold keys.

Learn more →
Hourly

Hypergap Support

Paid 1:1 setup, multisig design review, recovery rehearsal, threat-model consultation. A real human, scheduled, scoped. For users who want hand-holding through the dedicated-phone setup or a multisig inheritance design.

Book time →
Cosmetic

Hypergap Supporter

Donate and unlock alternate app icons, themes, accent colors, and a supporter badge in community channels. Pure cosmetics - every security feature stays free, forever, for everyone.

Become a supporter →
Donate

Fund the project

GitHub Sponsors, Geyser, Lightning address. Hypergap is and will remain free, open source, and unsubsidized by VC. Plebs fund plebs - your sats keep this project independent of investors who would want the wrong things from it.

Donate →

▸ Free forever guarantee: every security feature in Hypergap is free, every release of the signer is free, and no service above ever gates a security feature. Services overview →

// SECTOR / 11 - questions

Frequently asked.
Honestly answered.

Is a phone really safe as a hardware wallet?
Hypergap is not designed to run on the phone you carry every day. It runs on a dedicated, permanently-offline phone - factory-reset, signed out of every account, SIM removed, airplane mode locked on. In that configuration, modern iPhones (Secure Enclave, A12+) and Android devices (StrongBox / Titan M, Pixel 3+) provide hardware-grade key isolation comparable to dedicated hardware wallets. Hypergap stores keys inside that secure element so they are not exposed to the operating system, to us, or to other apps on the device. Combine that with permanent air-gap and you get a signer with a full-size verification screen, no supply-chain exposure, and zero cost.
Why a dedicated phone instead of my everyday phone?
Your everyday phone has a SIM card, network connections, dozens of installed apps, an active iCloud or Google account, biometric unlock tied to that account, and a constant attack surface. None of that is acceptable for cold storage. Hypergap assumes the phone running it has none of those things. Re-using a spare phone - a hand-me-down iPhone, an old Pixel - costs nothing, requires no shipping, and gives you a clean security boundary. The same boundary a Coldcard or a Trezor sits inside.
What phone do I need?
Any iPhone or Android from roughly the last six years works. The device needs a secure element (iPhone 6s+ with Secure Enclave; Pixel 3+ or recent Samsung flagship with StrongBox / Titan M), a working camera, and a working screen. No SIM, no service plan, no recent OS version strictly required.
How is this safer than just airplane-moding any wallet app?
Hypergap is built around the assumption that the device never reconnects. No networking. The only networking code is a detector which marks the device as compromised if it succeeds. The threat model is "hostile OS" rather than "trusted OS, hostile network." Most wallets that call themselves "cold" still ship network features with a flag flipped off; an OS-level exploit lifts the flag.
How does QR signing actually work?
Your online wallet (Sparrow, Specter, Zeus, etc.) builds an unsigned PSBT and renders it as an animated QR. Hypergap reads it via camera, shows you the decoded transaction on the offline phone - address, amount, fee, all human-readable - and renders the signature back as another animated QR. Your online wallet broadcasts. The only channel between online and offline is light on glass, one direction at a time.
Does Hypergap support multisig and Taproot?
Yes. Hypergap is a full PSBT signer with coordinator and cosigner roles for P2WSH, P2SH, and P2TR script-path multisig. BIP-48 descriptors. 2-of-3, 3-of-5, geographically distributed. Taproot key-path (Schnorr / BIP-340), Taproot script-path, and MuSig2 are all supported. BIP-322 message signing for proof-of-reserves and exchange ownership proofs.
What if I lose the phone?
Recovery is by seed, not by device. Hypergap offers four independent backup schemes: Shamir Secret Sharing, SSKR (Blockchain Commons), Seed XOR (Coldcard-compatible), and Hamming 2-of-3. Each share is a valid BIP-39 mnemonic. Choose a scheme - or mix schemes - based on your threat model, and distribute shares geographically. If the phone is lost, stolen, or destroyed, restore on any other dedicated phone running Hypergap, or on any wallet that supports the same standards.
What if someone forces me to unlock the signer?
Hypergap includes eight coercion-resistance modes: Wipe & Reboot, Silent Wipe, Open Decoy Wallet (a BIP-85-derived wallet with small funds), Brick Device, Show Countdown, Look Blank (the app appears freshly installed), Delta Mode (allows spending but blocks seed viewing), and Reboot-and-Wipe. Each mode has its own PIN. Under duress, entering the duress PIN you chose triggers the defense you chose. The seed itself is never displayed to an attacker.
Is Hypergap open source?
Yes. MIT licensed, every line public, releases reproducibly built. You can verify the binary on your phone matches the source on GitHub yourself - and we recommend you do. See <a href="/reproducible-builds">/reproducible-builds</a> for the recipe and <a href="/audits">/audits</a> for external review.
How does Hypergap compare to Ledger, Trezor, Coldcard?
Hypergap matches dedicated hardware on the security primitives that matter - hardware-isolated key storage, PIN authentication, on-device seed generation, air-gapped signing - and adds four backup schemes, eight duress PINs, verifiable dice and coin entropy, BIP-85 child wallets, geofence access, and a full-size verification screen. The trade-off is the dedicated-phone setup: thirty minutes of careful configuration up front, in exchange for $0 cost, zero supply-chain risk, and a device you can replace from any electronics store. See the comparison section above for a row-by-row breakdown.
How do you make money if the app is free?
The app is free. Optional services pay the bills: <strong>Hypergap Backup</strong> (encrypted cloud backup of wallet metadata, no key material), <strong>Hypergap Coordinator</strong> (hosted multisig coordinator, no custody), <strong>Hypergap Inheritance</strong> (dead-man's switch), <strong>Hypergap Support</strong> (paid 1:1 setup), <strong>Hypergap Supporter</strong> (cosmetic perks), and direct donations. No security feature is ever gated. No telemetry. No accounts. See the services section above.
Is there a desktop / web version?
Yes - for testing. A desktop binary and a web build exist so you can try Hypergap, read the source, and practice the QR flow before committing a spare phone. If you sign real transactions with them, the only setup we'd recommend is Tails booted from USB, with no persistent storage and networking disabled. For any meaningful balance, only a dedicated, network-isolated phone is the deployment we trust.

Begin offline.
Stay offline.

Coming soon. Free, open source, no signup, no telemetry. Star the repo to be there for the first release.

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