Cupcake: turn a spare phone into an air-gapped signer
Cupcake is a free app from the Cake Wallet team that keeps your private keys on a spare, offline phone and signs Monero, Bitcoin and Litecoin transactions by QR code. Cake Wallet on your everyday phone holds only view or public keys. It is cheaper than a hardware wallet, but an old phone is not a secure element, so its safety depends on how carefully you set it up.
Quick steps
- Prepare the spare phone. Factory reset it, update it, install Cupcake from the official store listing, then turn off Wi-Fi, mobile data and Bluetooth for good.
- Create the wallet in Cupcake. Pick the coin, choose Create new wallet, set a strong PIN or password and name the wallet.
- Back up the seed. Write the seed phrase on paper and complete the verification step. This phrase is the real backup.
- Show the link QR code. In Cupcake's menu choose Link to Cake Wallet to display a QR code.
- Add it in Cake Wallet. On your everyday phone open Wallets, tap Restore Wallet, choose Cupcake App, scan the QR code, name the wallet and tap Restore.
- Sign by QR. Build a transaction in Cake Wallet, scan its QR code with Cupcake, approve it there, then scan the signed QR code back into Cake Wallet to broadcast.
Cupcake is Cake Labs' answer to the cost and delivery hassle of hardware wallets. Instead of buying a device, you repurpose a phone you no longer use. It holds the keys and never goes online; your normal phone runs Cake Wallet as a view-only wallet. Transactions travel between the two as QR codes.
Key facts
| Item | Detail (October 2026) |
|---|---|
| Maker | Cake Wallet team; App Store publisher Cake Technologies, LLC |
| Price | Free and open source |
| Platforms | iOS and Android phones |
| Coins | Monero, Bitcoin, Litecoin including MWEB; Cake says more will follow |
| Connection | QR codes only, no cable, Wi-Fi or Bluetooth needed |
| History | Monero signing from Cake Wallet 4.21 (November 2024), Bitcoin from 5.2, Litecoin and MWEB from 5.6; announced widely in September 2025 |
Store identifiers, so you can check you have the real app: App Store id 6737430272, Android package com.cakewallet.cupcake. Only install from the official store listings or the project's GitHub releases. Do not confuse it with unrelated apps of the same name.
How it works
Every crypto wallet has keys that can see funds (view or public keys) and keys that can spend them (private or spend keys). Cupcake splits them across two phones:
- Cupcake creates the wallet and keeps the spending keys.
- Its "Link to Cake Wallet" QR code gives Cake Wallet only the viewing information, so your everyday phone can sync, show the balance and history, and prepare unsigned transactions.
- When you send, Cake Wallet shows the unsigned transaction as a QR code. Cupcake scans it, shows you the details, and signs.
- Cake Wallet scans the signed result and broadcasts it.
Because the spending keys never touch the online phone, malware there cannot steal funds on its own. It could still try to trick you into signing a transaction to the wrong address, so always check the address and amount on the Cupcake screen.
Cupcake compared with a hardware wallet
| Point | Cupcake | Dedicated hardware wallet |
|---|---|---|
| Cost | Free with a spare phone | Price of a device |
| Delivery and privacy | No order, no shipping address | Purchase and delivery records |
| Key protection | Phone's normal storage and OS security | Purpose-built device, often with a secure element |
| Attack surface | A full smartphone OS, possibly no longer updated | Minimal firmware |
| Coins in Cake Wallet | Monero, Bitcoin, Litecoin with MWEB | Depends on device; see Ledger and Trezor |
Not everyone is convinced. In a November 2025 Privacy Guides forum discussion, some contributors said they would not call it a hardware wallet at all, argued that phones which no longer get security updates are exposed to known exploits, and that many users may not set it up correctly. Others pointed to the cost, privacy and open-source benefits. Both sides have a point: Cupcake is clearly better than keeping large sums in a hot wallet on your daily phone, and a reputable hardware wallet is a stronger choice when the amount justifies it.
Setting it up well
- Use a phone that still gets security updates if you can. Factory reset it first.
- Keep it offline permanently. After installing Cupcake, turn on airplane mode and turn off Wi-Fi and Bluetooth. Do not sign in to cloud accounts or install other apps.
- Use a strong PIN or password on both the phone and Cupcake.
- Back up the seed on paper. If the spare phone breaks, the seed restores the wallet in Cupcake on another phone or in any compatible wallet.
- Test with a small amount, including one full send and sign, before moving savings.
- Store the phone safely. Anyone who gets it and its PIN can spend.
Who Cupcake suits
Cupcake makes the most sense for people who hold more Monero, Bitcoin or Litecoin than they would keep on a daily phone, already have a spare phone, and either cannot easily buy a hardware wallet or prefer not to leave a purchase and delivery record. It is also a practical way to learn how air-gapped signing works before buying hardware.
It suits less well if you hold coins Cupcake does not support, if your only spare phone is very old and no longer updated, or if you are likely to reconnect the signer to the internet out of convenience. In those cases a dedicated device is the safer choice; see our hardware wallet guide. For small spending amounts, a normal Cake Wallet on your phone with a good backup is usually enough.
Limits to know
- Coins are limited to Monero, Bitcoin and Litecoin for now.
- Features that need private keys in Cake Wallet, such as Lightning, are not available for view-only wallets.
- Every send takes a few QR scans, so it suits savings rather than daily spending.
- Keeping an offline phone's apps up to date takes deliberate effort; plan how you will update Cupcake before you rely on it.
Cake Wallet never asks for your Cupcake seed and never messages you first. Keep the seed off both phones' cameras and clipboards.
Frequently asked questions
Is Cupcake free?
Yes. Cupcake is a free, open-source app. You only need a spare iOS or Android phone.
Which coins does Cupcake support?
Monero, Bitcoin and Litecoin including MWEB, as of October 2026. Cake says more coins will be added.
Is Cupcake as safe as a Ledger or Trezor?
Not in the same way. It keeps keys offline, but a phone lacks a hardware wallet's secure design and old phones may miss security updates. It is a big step up from a hot wallet, not a full replacement for dedicated hardware.
What happens if the Cupcake phone breaks?
Restore the Cupcake seed on another phone in Cupcake, or in any wallet that supports that seed, then link it to Cake Wallet again.
Can Cupcake be used without Cake Wallet?
Cupcake is designed as the signer for Cake Wallet. Your seed is standard for its coin, so funds can always be restored in other compatible wallets.