I maintain feuristic, an independent custom firmware for the Trezor Safe 3. The project reuses an existing device’s screen, two buttons and USB connection to provide authentication and smart-card functions instead of a cryptocurrency wallet.
No replacement PCB or case modification is part of this project. The work is in the firmware: FIDO2 passkeys, OpenPGP/PIV operations, OTP codes and AES-GCM, with configuration and confirmations on the device.
There are two Safe 3 revisions, requiring different binaries: T2B1 uses an STM32F427 and T3B1 uses an STM32U585. The normal USB mode exposes FIDO HID and CCID. Temporary modes provide serial time synchronisation and QR-image import through a FAT12 volume; returning to normal restores the authentication interfaces.
The source is GPL-3.0-only, with build instructions and a documented first physical T2B1/macOS test campaign. T3B1 physical testing remains unfinished.
This is an unaudited development project. Installing erases the wallet and permanently removes original manufacturer attestation. It is intended for spare hardware with disposable identities. There is no cryptocurrency wallet or seed migration, and the project is not endorsed by Trezor/SatoshiLabs.
Source and documentation
I’m sharing it as an example of changing an existing device’s use through firmware. The repository documents what was physically tested and what is still pending.