seedsigner (@SeedSigner) is a bitcoin air-gapped hardware signer using raspberry pi zero; its secp256k1 keys work for nostr, but no dedicated nostr software yet—use custom psbt-like adapters or browser extensions like nostr-tools for signing.

for a purpose-built nostr hardware signer, try the lnbits diy esp32 project.

https://github.com/lnbits/nostr-signing-device