Air gap
An air-gapped signing device has no cable or wireless connection to other devices. Transactions travel back and forth by QR code or memory card – so the private key stays completely offline.
Alsoair-gappedairgapoffline signingair-gapped signingair-gapped signer
On the learning path: Stage 6 · Step 1 – Hardware wallets compared
An air gap is literally a gap of air: the device holding your private keysGlossaryPrivate keyA secret, randomly generated number that you use to sign transactions and so control your bitcoin. Anyone who knows the private key can spend the bitcoin that belongs to it – it must never fall into anyone else’s hands.On the learning path: Stage 5 · Step 3 – Backing up your seed phrase →In the glossary → has no data cable, no Wi-Fi and no Bluetooth. Data only crosses over deliberately – by QR code or memory card.
How a payment works
Prepare
The wallet app on your computer or phone creates the payment as a PSBTGlossaryPSBT (partially signed Bitcoin transaction)A standard format for Bitcoin transactions that are not yet fully signed. It lets a wallet app, a hardware wallet and co-signers pass a payment between them without sharing private keys.On the learning path: Stage 6 · Step 1 – Hardware wallets compared →In the glossary → – as a QR code or as a file on a microSD card.Check and sign
The offline device reads it in. You check the recipient and amount on its display and confirm.Return and broadcast
The signed transaction goes back the same way, and the app sends it to the network.
Thanks to PSBT, the signing device never has to be connected to another device.[1]
Pros and cons
- For: There is no permanent data channel through which malware could reach the device.
- Against: Every payment takes a few more steps. An air gap doesn’t protect you from a lost backup or from a scammer who talks you into making a payment.
One example is the open-source SeedSignerProvider · Hardware walletSeedSignerOpen-source DIY signing device: Raspberry Pi Zero, camera, small display – Bitcoin-only, no key storage, QR only.Open-source project – no company, no financial licence · reviewed Sept 2026Price: Parts usually under $50 (project’s figure) (as of Sept 2026)On the learning path: Stage 6 · Step 1 – Hardware wallets compared →Our profile →Official website ↗Only buy hardware wallets from the manufacturer or an authorised reseller.: no Wi-Fi or Bluetooth, communication by QR code only, no permanently stored keys.[2] You scan or type in your seed phrase again each time you use it.
Related terms
These terms are closely connected.
- This termAir gap
- Hardware walletA small dedicated device that keeps your private keys offline and signs transactions internally. The key never leaves the device, so malware on your computer can’t get at it.
- PSBT (partially signed Bitcoin transaction)A standard format for Bitcoin transactions that are not yet fully signed. It lets a wallet app, a hardware wallet and co-signers pass a payment between them without sharing private keys.
- Cold storageStoring bitcoin in a way that keeps the private keys from ever touching the internet – for example on a hardware wallet or an offline device. It protects against online attacks, but requires a carefully kept backup.
- Secure element (security chip)A chip specially hardened against physical attacks, like the ones in bank cards and passports. In many hardware wallets it protects the PIN and secrets if the device falls into the wrong hands.
- Private keyA secret, randomly generated number that you use to sign transactions and so control your bitcoin. Anyone who knows the private key can spend the bitcoin that belongs to it – it must never fall into anyone else’s hands.
Explained in depth
These articles go into more detail:
- Stage 6 · Step 1Hardware wallets comparedBitBox, Trezor, Jade, COLDCARD, Ledger and SeedSigner compared: open code, security chip, air gap, display, prices – and every major incident.
- Deep dive · Stage 6Setting up a hardware walletSet up a hardware wallet safely: buy from the manufacturer, check the seal and authenticity, write down the seed phrase, set a PIN and confirm every address on the device.
More from „Wallets & security“
Sources2 sources · 2 publishers
The superscript numbers in the text refer to these sources.
- External signers – Bitcoin Design Community – Bitcoin Design Guide (accessed 28/09/2026)
- SeedSigner – Build an offline, airgapped Bitcoin signing device – SeedSigner (open-source project) (accessed 28/09/2026)
This entry is for education only and is not investment, tax or legal advice.