OpenDime
Physical Bitcoin bearer instrument - load BTC onto a USB stick and pass it like cash until unsealed to spend.
Why We Recommend OpenDime
OpenDime operates as a fully self-custodial device where the private key is generated inside the hardware using 256KB of user-provided random data combined with the device's serial number and internal hardware random number generator. The key remains completely unknown and inaccessible until the device is physically unsealed by breaking a resistor, making it impossible for anyone, including the manufacturer Coinkite, to access funds on a sealed device.
The device includes a dedicated secure element for hardware-based key storage and features tamper-evident design with a transparent cover that makes any physical modification immediately visible. Coinkite, the manufacturer, also produces the well-regarded Coldcard hardware wallet and has established credibility in the Bitcoin hardware security space. The firmware is fully open-source on GitHub with reproducible builds, and a 75-line Python verification script allows users to audit the key generation process. No security incidents, exploits, or counterfeits have been reported, with the design claiming it would cost over $100 million to extract the factory key needed to create fakes.
Best For
OpenDime is ideal for Bitcoin users who want to transfer value physically without on-chain transactions, similar to handing over cash. This makes it perfect for in-person trades, gifting Bitcoin to friends or family, or introducing newcomers to cryptocurrency through a tangible, easy-to-understand format.
Long-term holders benefit from the simple cold storage model where funds remain completely offline and inaccessible until intentionally unsealed. The device works with any USB-compatible computer, phone, or tablet without requiring apps, accounts, or technical setup, making it accessible to beginners while still appealing to privacy-conscious users who want off-chain transfers with zero fees and no blockchain records between handoffs.
The low per-unit cost of approximately $12-16 makes it practical for storing moderate amounts of Bitcoin or creating multiple physical bearer instruments for different purposes.
Services & Features
- Bitcoin-only bearer instrument
- One-time-use USB stick design
- Tamper-evident sealed private key
- Off-chain physical transfers
- Works with any USB device
- Open-source firmware verification
- Compatible with Electrum and Bitcoin Core
- No apps or accounts required
Considerations
Once unsealed to access the private key, the device can never be trusted as a bearer instrument again. If lost or destroyed while sealed, funds are unrecoverable with no seed phrase backup. Best suited for moderate amounts rather than large holdings due to physical access risks.
