Coldcard Mk4
Hardcore Bitcoin-only air-gapped signer with deep power-user features and a steep learning curve.
Overview
The Coldcard Mk4 is the signer of choice for hardcore, Bitcoin-only self-custodians. Made by Coinkite, it deliberately does one thing — secure Bitcoin — and does it with more paranoid, power-user features than almost anything else. It supports true air-gapped operation via microSD card, so you can sign transactions without ever plugging it into a computer, and it uses dual secure elements to raise the bar for physical attackers.
What sets the Coldcard apart is depth: PSBT-based air-gapped workflows, a 'trick PIN' feature that can wipe the device or open a decoy wallet under duress, BIP-85 seed derivation, and first-class multisig support. Its firmware is open-source and it's built by a company with a long, credible Bitcoin track record.
The honest downsides are real. The learning curve is steep — the small screen and keypad and the sheer number of options can overwhelm beginners, and mistakes in advanced modes can be costly. It's Bitcoin-only, so there's no altcoin support at all. And its numeric keypad plus tiny display are less pleasant than the touchscreen-and-QR experience of the newer Coldcard Q. If you want ease and a big screen, look at the Q or a Foundation Passport. But if you want the most control-oriented, battle-tested air-gapped Bitcoin signer and you're willing to learn it, the Mk4 is a benchmark device.
Key features
- True air-gapped signing via microSD (PSBT) — never needs a computer
- Dual secure elements for layered physical-attack resistance
- Bitcoin-only firmware, open-source
- Duress and 'trick' PINs that can wipe or open decoy wallets
- Strong multisig and BIP-85 seed-derivation support
- USB-C also available for those who want it
- Made by Coinkite, a long-established Bitcoin hardware maker
Specs
- connection USB-C + microSD (air-gap)
- open Source Yes
- secure Element Yes
- bitcoin Only Yes
Who it’s for
Serious Bitcoiners who want maximal control and don’t need altcoins.
Watch: hands-on videos
Coldcard Mk4: frequently asked questions
Is the Coldcard Mk4 hard to use for beginners?
Yes. It's powerful but has a steep learning curve, a small screen, and many advanced options. Newcomers often find a Foundation Passport or Trezor easier to start with.
Can it hold altcoins?
No. It is deliberately Bitcoin-only. That reduces attack surface and complexity, but means no support for other coins.
How does air-gapped signing work?
You move unsigned transactions (PSBTs) to the device on a microSD card, sign offline, and carry the signed file back — the Coldcard never has to touch an internet-connected machine.
What's the difference between the Mk4 and the Coldcard Q?
The Q adds a full QWERTY keyboard, a QR scanner for air-gap, a bigger screen, dual SD slots, and a battery. The Mk4 is smaller and cheaper with a numeric keypad.
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