Air-gapping usually means giving up chain coverage — the Bitcoin-only devices dominate that niche. Keystone breaks the trade-off: the same QR-only isolation, with support for Ethereum, Solana, Cosmos chains, Bitcoin and a long list of tokens, plus integration with MetaMask, Rabby, Keplr and others.
How QR signing works
The wallet software on your phone or computer displays an unsigned transaction as a QR code. The Keystone reads it with its camera, decodes it on screen, you approve, and it displays the signed transaction as a QR code the software reads back. No cable, no radio, no USB stack. Slower than plugging in, and one entire class of attack surface removed.
Verification quality
The touchscreen decodes contract interactions into readable form rather than showing a hash, which is what makes air-gapping worthwhile — an isolated device that cannot tell you what you are approving does not solve the actual problem. Fingerprint unlock and a self-destruct mechanism on physical tampering round out the hardware.
The openness gap
Firmware is partially open: more than Ledger, less than Trezor or BitBox. That is the main reason it does not score higher, and it is a reasonable trade for the chain coverage if you weight functionality over full verifiability.
Who should use it
Multi-chain users who want air-gapped security, DeFi users who need readable contract decoding on a large screen, and anyone whose threat model includes a compromised computer.