ONLINE
Load your value.
Deposit USDC on Ethereum to create a digital banknote. In under 1 minute, it carries a proof that its funds exist and is ready to spend offline.
Cash, without
the connection.
Money should move when you do.
Pay with stablecoins, directly between nearby devices.
No internet needed, for either side, at the moment of payment.
AndroidiOSWear OSwatchOSWORKING PROTOTYPE
NO SIGNAL.
STILL PAYING.
STILL PAYING.
Banknotes + coinsTwo ways to carry value
Offline by design
The receiver checks the money is real offline, then can spend it again immediately.
Hardware-backed
Each key signs exactly once, enforced by secure hardware.
Settled on-chain
Deposits and redemptions are ordinary blockchain transactions.
01 — THE PAYMENT FLOW
Load it. Pass it.
Cash it out.
Stablecoins become digital cash you can carry. Value moves directly between devices without internet or an existing Wi-Fi network, and returns on-chain when someone redeems it.
Any stablecoin. Any EVM-compatible blockchain. The working prototype uses USDC on Ethereum Mainnet. The payment flow below shows that example.
OFFLINE
Pay, person to person.
Phones connect directly to each other using Bluetooth and device-to-device Wi-Fi. No router or existing Wi-Fi network is needed. The receiver checks the banknote's proof on the spot, and secure hardware makes sure the same value can't be spent twice. Banknotes and coins you receive can be spent again immediately, still offline.
ONLINE
Redeem on Ethereum.
Select the banknotes and coins you want to cash out and redeem them together on Ethereum in one online transaction.
Online at the edges, offline in between: deposit and redemption need a connection; the payments in between don't.
How does the receiver know it's real?
Every banknote carries a compact proof that its deposit exists on Ethereum, signed by Ethereum's own validators. The receiving phone checks it in milliseconds, with no internet and no server to trust. If the payer's phone has newer validator information, it hands it over during the payment, so the receiver never needs to go online.
The proof is built once, in under 1 minute, and travels with the money from then on.
Pay the right phone.
When two phones connect, both screens show an image of a robot and six digits. The payer checks they match before anything is sent, so money can't go to the wrong device nearby.
02 — A NEW KIND OF WALLET
A little cash.
A lot of character.
A digital banknote can look like something worth keeping. Give it a custom face, a personal image, or even an animation.
Banknotes with personality
Distinct notes carry value and a face of your choosing. Receive one and spend it again immediately, even offline.
Coins for the exact amount
Turn a banknote into coins in your coin purse, then pay any amount. Received coins can be spent again immediately, even offline, or redeemed on Ethereum in full or in part.
Illustrative banknote artwork from the prototype. The face is decorative: the printed number isn't the value. The app shows each banknote's real USDC value.
03 — PRIVACY, BY CHOICE
Your payment.
Your privacy.
Two ways to pass a banknote: a signed payment chain with one-time keys, or a direct key handoff using an eSIM or NFC sticker.
ONE-TIME PAYMENT KEYSPatent pendingThe journey is verified.
The journey is verified.
The keys are one-time.
Each payment adds a signed entry to the banknote's payment chain, using a fresh key that isn't linked to anyone's identity. When the banknote is redeemed, the chain is presented to Ethereum and becomes public, but it shows one-time keys, not people.
The payment itself happens offline. The chain becomes visible only on redemption.
PASSING A BANKNOTESTANDARD MODE
Holder ASecure hardware
Signed handoff
→
A new chain entryHolder BSecure hardware
Ethereum redemptionPayment chain checked in one redemption transaction
Deposit and redemption are on-chain in both modes. High privacy adds no new entries; it doesn't remove earlier ones.
04 — SECURE WHERE IT MATTERS
One owner.
At a time.
HeisenCash uses built-in secure hardware on Android and iPhone to stop a previous holder from spending the same value again. The new holder can spend it immediately, still offline. No extra hardware is needed for standard payments.
The security is already inside.
On Android, your phone's built-in secure hardware supports offline payments at Security Levels 1–4. An optional eSIM or NFC sticker adds Level 5, the highest security level, and enables High Privacy banknote transfers. NFC stickers work on both Android and iPhone; eSIM support is Android-only for now.
Standard payments work without either add-on.Built-in. Ready to pay.
On iPhone, payment keys are generated inside the built-in Secure Enclave, with attestation to verify their origin. An optional NFC sticker adds Level 5, the highest security level, and enables High Privacy banknote transfers. iPhone-to-iPhone payments use the direct wireless technology behind AirDrop.
Standard payments work without an NFC sticker.Cash, a little closer.
Send and receive coins from your wrist on Android and Apple watches, protected by the watch's secure hardware and screen lock. Banknotes are turned into coins when they arrive.
Part of the cross-device working prototype.No central contract. No server.
Redeem any number of banknotes and coins together in one online transaction, shown on-chain as a single contract interaction. No central payment contract or HeisenCash server is needed.
05 — ALREADY TAKING SHAPE
From an idea
to in your hand.
A working prototype for Android phones, iPhone, Android watches and Apple Watch, tested with real USDC on Ethereum Mainnet. Banknotes, a coin purse and device security come together in one payment experience.
These are actual prototype screens with test balances. Switch both phones between Home and Wallet, or select a screen to take a closer look.
A FEW GOOD QUESTIONSThe details
The details
that matter.
Which stablecoins and blockchains work with HeisenCash?
HeisenCash works with any stablecoin on any EVM-compatible blockchain. The working prototype uses USDC on Ethereum Mainnet. The Ethereum examples and timings on this site describe that setup.
What does "offline" actually mean?
The payment itself needs no internet on either phone. The phones connect directly to each other using Bluetooth and device-to-device Wi-Fi, without a router or an existing Wi-Fi network. iPhone-to-iPhone payments use the direct wireless technology behind AirDrop. Depositing USDC and redeeming it on Ethereum need a connection. A new deposit becomes spendable offline in under 1 minute.
Can I spend received money again while still offline?
Yes. Banknotes and coins you receive can be spent again immediately, and the next person can do the same. You don't need to go online or redeem them between payments.
How does the receiver know the money is real?
Every banknote carries a proof that its deposit exists on Ethereum, signed by Ethereum's own validators. The receiving phone checks it offline in milliseconds. If the receiver happens to be online, it also checks the balance on Ethereum directly.
How is double spending prevented?
Every key can sign exactly once, and secure hardware enforces it. Android uses the phone's built-in secure element or Trusted Execution Environment (TEE) at Security Levels 1–4. iPhone generates and attests payment keys in its built-in Secure Enclave. Neither platform needs an eSIM or NFC sticker for standard payments. These optional upgrades add Level 5, the highest security level: an NFC sticker on Android or iPhone, or an eSIM on Android only for now. High Privacy banknote transfers require one of these upgrades on each device. Once a banknote has been paid, the key that controlled it can't sign again.
What does Ethereum see?
Deposits and redemptions. You can redeem any number of banknotes and coins together in one transaction, shown on-chain as a single contract interaction. The transaction remains in Ethereum's history. In standard mode, the payment chain is presented on redemption and shows one-time keys, not people. High Privacy moves the key between devices' secure hardware without adding a new payment-chain entry. Offline payments themselves never touch Ethereum.
How do I know I'm paying the right phone?
Both screens show an image of a robot and six digits. The payer confirms they match before anything is sent.
What's the difference between banknotes and coins?
Banknotes are individual pieces of digital cash with custom faces. A banknote can be turned into coins in your coin purse, which lets you pay any amount. Coins can be redeemed on Ethereum, in full or in part.
Can I download HeisenCash today?
Not yet. HeisenCash is a working prototype for Android phones, iPhone, Android watches and Apple Watch. Public downloads aren't available yet. Check availability for your device.
Stablecoins,
out in the world.
For the moments between connections.
For value that moves person to person.