Crypto glossary
Air-gapped wallet
An air-gapped wallet signs transactions on a device that never connects to the internet, USB or Bluetooth, passing data only via QR codes or microSD cards.
Air-gapping means physically isolating a device from any network. An air-gapped wallet generates and stores its keys on such a device. To spend, a connected companion app builds an unsigned transaction, often as a PSBT for Bitcoin, and shows it as a QR code or writes it to a microSD card. The offline device reads it, displays the details for checking, signs, and returns the signed transaction the same way for broadcasting.
The goal is to close the channels malware uses to reach keys. Several hardware wallets designed for long-term Bitcoin storage work this way, and some people build air-gapped setups from old laptops or single-board computers. Institutions use similar ceremonies for their deepest cold storage.
Air-gapping reduces attack surface but does not remove every risk. A tampered device from the supply chain, firmware with a flaw in its random number generator, or a user who skips verifying the address on the screen can all defeat it. The process is also slower and less convenient than a USB hardware wallet, which matters for frequent transactions.
Example
To move savings, a user creates a PSBT in desktop software, scans its QR code with an air-gapped signer, checks the amount and address on its screen and scans the signed result back.