Open‑Source Device Generates Bitcoin Seed Phrases from Radioactive Decay

An open‑source hardware project called Entropy32 Plus converts the timing of radioactive decay events into standard 12‑word or 24‑word Bitcoin recovery phrases. The device operates completely offline, using a Geiger counter as its physical source of randomness and a microcontroller to process the data.

How the device works

The system receives pulses from a GQ Electronics GMC‑320S Geiger counter through a 3.5 mm connector. An LM393 comparator digitises each pulse, and an ATmega328P microcontroller records the interval between successive events with a microsecond timer. The firmware compares each new interval with the previous one, outputting a ‘1’ when the interval is longer and a ‘0’ when it is shorter; equal intervals are discarded. Intervals under 200 µs are ignored as possible glitches. This process continues until 512 comparison bits are collected.

Hash conditioning and BIP‑39 conversion

Once the 512‑bit pool is filled, the firmware hashes the data with an internal SHA‑256 implementation. For a 12‑word phrase the first 16 bytes of the hash are used; for a 24‑word phrase the full 32 bytes are used. The resulting bits are mapped to the BIP‑39 English wordlist according to the standard specification, producing a mnemonic that can restore a Bitcoin wallet.

Offline design and data handling

The generator has no wireless interfaces. Users interact via two buttons and read the generated phrase on a 0.91‑inch OLED screen. The phrase is stored only in RAM and is overwritten after the user confirms it, along with all intermediate buffers. No persistent storage or secure element is included, and the firmware does not verify that the device’s hardware matches the published code.

Unvalidated entropy source

The developer notes that the Geiger‑counter source has not been evaluated under NIST SP 800‑90B or any independent audit. The README recommends mixing the Geiger‑derived data with another validated source before using the seed for valuable funds. As of the latest repository snapshot (September 13, 2026), no raw‑event dataset, NIST assessment, or third‑party audit is provided.

Security considerations

While the offline architecture removes network‑based attack vectors, the lack of source‑code verification and untested entropy means a maliciously modified unit could output predetermined phrases or retain data. Users are advised to treat the device as experimental and avoid using it for significant amounts of Bitcoin until an independent review is completed.