What is air-gapped wallet?

A wallet kept on a device that never connects to the internet, signing transactions offline and passing them out by QR code, memory card, or cable.

Air gapping removes the main path a remote attacker uses to reach your keys. It does nothing about a lost backup or a signature you were tricked into making. See cold wallet and hardware wallet.

The term gets used loosely. A hardware wallet plugged into a laptop by USB is cold storage but not air gapped, because a channel exists between the signing device and an internet-connected machine. A true air gap means the only thing crossing the boundary is a signed transaction you can inspect.

How it works

The signing device holds the keys and never joins a network. A separate, connected device runs a watch-only copy of the wallet, which knows your addresses through an extended public key such as an xpub but holds no secret.

The connected device builds an unsigned transaction. On Bitcoin this is usually a partially signed transaction in the format specified by BIP-174, which carries everything the offline device needs to understand what it is signing.

You move that unsigned transaction across the gap by displaying a QR code, writing to a memory card, or animating a sequence of codes for larger payloads. The offline device shows the destination and amount on its own screen, you approve, and it produces a signature.

The signed transaction goes back the same way and the connected device broadcasts it. The private key never exists on any machine that has ever had a network connection.

Example

Illustrative: you hold 0.5 BTC. Your laptop runs a watch-only wallet built from an xpub and can see the balance but cannot spend. To send 0.1 BTC you build the transaction on the laptop, scan the QR code with the offline signer, read the destination on the signer's screen, approve, scan the signature back, and broadcast. An attacker with full control of the laptop can see your balance and can propose transactions, but cannot produce a valid signature.

Why it matters when you buy

Air gapping is for the balance you intend to hold rather than trade, so it fits a buyer who accumulates on an exchange and sweeps to cold storage periodically. It adds friction to every spend, which is the point. Weigh that against withdrawal costs, since sweeping frequently in small amounts wastes fees; see the fee comparison and the guide on moving crypto off an exchange.

Related terms

• cold wallet — the broader category of offline storage
• hardware wallet — the usual signing device
• psbt — the format that crosses the gap
• watch only wallet — the connected half of the setup
• xpub — how the online side tracks addresses
• seed phrase — the backup that still has to be protected

Questions

Is a USB hardware wallet air gapped?

No. It is offline storage, but the USB link is a channel to an internet-connected computer. Devices that sign only over QR codes or memory cards are the air-gapped category.

Does an air gap protect against a stolen seed phrase?

Not at all. Anyone who reads your recovery phrase can rebuild the wallet elsewhere. The gap defends against remote compromise of the signing device, nothing more.

Do I need this for a small balance?

Probably not. The friction is real and the setup has more ways to go wrong. A well-backed-up hardware wallet covers most buyers; air gapping suits larger holdings and longer horizons.