All major cryptocurrency hardware wallets on the market either use general purpose microcontrollers that are never meant to be used as secure devices or break the Kerckhoffs's principle by using chips that require an NDA, thus making it impossible to completely release the source code. HWallet (https://gitlab.com/nemanjan/hwallet) is a project developed as a proof of concept to show that it is possible to have a very secure microcontroller, signing Bitcoin transactions in hardware and still be completely open source. The code is released under GPLv3 and is meant to serve as the basis for some future devices or projects aiming to connect the real world to blockchain. This talk will give a brief introduction to the project and describe ways for it's customization.