An open-source Bitcoin device is using radioactive decay as a source of randomness to generate 12-word and 24-word Bitcoin recovery phrases without an internet connection.
Called Entropy32 Plus, the experimental device measures the timing of radiation events detected by a Geiger counter. It then turns those measurements into random bits, processes them with SHA-256 and uses the result to create a standard BIP39 recovery phrase.
The project was published by developer Alexander Higgins in September 2026. Its open-source files include the firmware, circuit-board designs, manufacturing files and a printable enclosure.
The device connects to a Geiger counter and measures the time between radiation events. Because radioactive decay happens unpredictably at the atomic level, the project uses those timing differences as its physical source of randomness.
The firmware compares consecutive time intervals and turns the results into zeros and ones. It continues collecting data until it has 512 comparison bits. Very short measurements and repeated intervals are rejected to reduce possible errors.
Once the 512-bit pool is collected, the device processes the data through SHA-256. It then uses part of the resulting hash to create either a 12-word or 24-word BIP39 recovery phrase.
The project says the hashing step can help reduce patterns caused by the detector, such as timing effects and changes in radiation count rates. However, hashing does not prove that the original data contained enough unpredictable information.
The device also includes a basic SHA-256 self-test. Before collecting entropy, it checks whether its SHA-256 implementation produces the expected result for a known test input. Passing this test only confirms that the hashing function works correctly; it does not prove that the radiation source provides enough entropy.
The generated data is then converted into BIP39 words. The 12-word version uses 128 bits of conditioned data plus a checksum, while the 24-word version uses 256 bits plus a larger checksum.
The device stores the BIP39 English wordlist directly in its firmware. The project says the wordlist, display system, hashing code and other functions use almost all of the available memory on the microcontroller.
Entropy32 Plus is designed to remain offline. It does not include Wi-Fi or Bluetooth, and the generated words are kept temporarily in the device’s RAM rather than being stored permanently.
After recording the recovery phrase, the user can activate a wipe process that overwrites the stored word data and starts the entropy collection process again. Temporary data used during the generation process is also cleared.
However, being offline does not automatically make the device secure. A modified device could potentially display predetermined words or secretly retain generated data. The project also does not include a secure element or a system that proves the installed firmware is the same as the publicly available code.
The biggest concern is the quality of the entropy itself. The developer says the Geiger-based entropy source has not yet been independently tested under NIST’s SP 800-90B standards.
The project recommends collecting a large amount of raw radiation timing data and testing it using appropriate entropy estimators. It also warns users to verify the entropy source themselves and use the device at their own risk.
The developer recommends combining the Geiger-generated data with another independently tested source before using the device to create a wallet containing valuable funds.
As of September 13, the project had not received an independent security audit or a formal NIST assessment. It also had no tagged production release or announced date for completing an independent security review.
For now, Entropy32 Plus remains an experimental open-source project rather than a proven secure method for generating Bitcoin wallets. Its approach is unusual, but the security of the resulting seed phrases ultimately depends on whether the radioactive-decay measurements provide enough reliable and unpredictable entropy.
