Coldcard Mk4: Complete Setup Guide for Bitcoin Holders

What Is the Coldcard Mk4

The Coldcard Mk4 is a hardware wallet made by Coinkite, a Canadian company that has focused exclusively on Bitcoin security products since 2013. Unlike multi-coin wallets that support dozens of tokens, the Coldcard supports Bitcoin only. That single-asset focus allows the development team to harden the firmware and hardware specifically for Bitcoin without the complexity that comes with supporting other networks.

The Mk4 is the fourth generation of the Coldcard line. It added a USB-C port, a faster secure element, and support for two separate secure chips from different manufacturers, which reduces the risk of a supply-chain attack compromising your keys. The device runs entirely on open-source firmware, and the hardware design files are also publicly available for review.

If you are new to hardware wallets in general, it is worth reading our hardware wallets explained guide before continuing. That article covers the basic concept of how a hardware wallet keeps your private keys offline and why that matters for long-term Bitcoin storage.

The Coldcard is not the easiest hardware wallet on the market. Devices like the Trezor Safe 5 or the Ledger Nano X have more polished consumer interfaces. But the Coldcard is designed for users who want to understand exactly what is happening with their keys and who want features like air-gapped transaction signing, duress PINs, and multisignature support built in from the start. If you want to compare options before committing, see our best hardware wallets guide for a broader overview.

What You Need Before You Start

Before you power on the Coldcard Mk4 for the first time, gather the following items. Having everything ready prevents interruptions during the setup process, which matters because you will be generating and recording a seed phrase that you cannot afford to lose or expose.

• Coldcard Mk4 device purchased directly from Coinkite or a verified reseller. Check the tamper-evident bag for any signs of opening before you begin.
• USB-C cable or power bank. The Coldcard can operate entirely without a computer using a USB power adapter, which is the preferred method for an air-gapped setup.
• MicroSD card. A card between 1 GB and 32 GB formatted as FAT32 works reliably. The Coldcard uses the SD card to export wallet files and sign transactions without a USB data connection.
• Pen and durable paper for writing down your seed phrase. Some users prefer a metal seed backup product for fire and water resistance. Do not photograph your seed phrase or store it digitally.
• Sparrow Wallet installed on your computer. Sparrow is a free, open-source Bitcoin wallet for desktop that pairs well with the Coldcard and gives you full control over your transactions.

You do not need to connect the Coldcard to the internet at any point during setup. That is one of its core security properties. Understanding the difference between cold storage and a connected wallet is important context here. Our article on cold storage vs. hot wallets explains why keeping your keys offline is worth the added steps.

First Boot and PIN Setup

Connect your Coldcard Mk4 to a USB power source. A USB wall adapter or power bank works well here. You should see the Coldcard logo and a brief startup sequence. The device will prompt you to check the bag number against what is printed on the tamper-evident packaging. Verify that number matches before proceeding.

Setting Your PIN

The PIN on a Coldcard is split into two parts: a prefix and a suffix. This two-part structure enables an anti-phishing feature. After you enter your prefix, the Coldcard displays two words from its word list. Those words are unique to your specific device and PIN prefix. Every time you log in, you should see those same two words before entering your suffix. If the words ever change, something is wrong with the device or you are entering the wrong prefix.

To set your PIN, navigate to New Wallet and follow the prompts. You will be asked to choose a prefix PIN of 2 to 6 digits, confirm it, then choose a suffix PIN of 2 to 6 digits, and confirm that as well. Write down your anti-phishing words somewhere you will remember them. These words are not a secret, but you need to recognize them each time you unlock the device.

Duress PIN

The Coldcard also supports a duress PIN. If you are ever forced to unlock your wallet under pressure, entering the duress PIN opens a decoy wallet with a separate balance. Setting up a duress PIN is optional during initial setup, but it is worth considering if you hold a significant amount of bitcoin. You can configure it later from the settings menu.

Once your main PIN is set, the device will bring you to the main menu. Take a moment to familiarize yourself with the navigation. The number keys move through menu items, and the checkmark and X keys confirm or cancel selections.

Generating and Backing Up Your Seed Phrase

From the main menu, select New Wallet if you have not already done so. The Coldcard will generate a new 24-word seed phrase using its internal random number generator combined with input from the secure elements. You can optionally add dice rolls to the entropy at this stage, which some users prefer as an additional source of randomness.

Writing Down Your Seed Phrase

The device will display your 24 words one at a time. Write each word down carefully, in order, on paper. Number each word. When you have written all 24, the device will quiz you by asking you to enter specific words from your list. This confirmation step verifies that you recorded the words correctly.

Your seed phrase is the master backup for your bitcoin. Anyone who has those 24 words can reconstruct your wallet and access your funds on any compatible wallet software. Store the backup in a secure physical location, separate from the Coldcard device itself. Many holders keep a copy in a home safe and a second copy in a separate secure location.

If you are not familiar with how seed phrases work or why they are so important, our article on what is a seed phrase covers the concept in detail. Understanding this before you proceed is worth the time.

Metal Backup Options

Paper degrades over time and is vulnerable to fire and water. A metal seed backup plate, where you stamp or engrave your words into steel or titanium, provides much better long-term durability. Several products are compatible with the standard 24-word BIP39 format that the Coldcard uses. This is not required for initial setup, but it is a worthwhile upgrade for anyone holding bitcoin as a long-term store of value.

Once you have confirmed your seed phrase, the Coldcard will return to the main menu. Your wallet is now initialized.

Using the Optional BIP39 Passphrase

The BIP39 passphrase is an optional 25th word that you choose yourself. It is not stored on the device. When combined with your 24-word seed, it produces an entirely different wallet with a different set of addresses. This means that even if someone finds your written seed phrase backup, they cannot access your bitcoin without also knowing the passphrase.

To add a passphrase on the Coldcard Mk4, go to Passphrase from the main menu. Enter your chosen passphrase and confirm it. The device will show you a fingerprint, which is a short code derived from the resulting wallet. Record that fingerprint alongside your passphrase so you can verify you are entering it correctly in the future.

Important Considerations

• The passphrase is not recoverable. If you forget it, your bitcoin in that wallet is permanently inaccessible. Store it with the same care as your seed phrase, but in a separate physical location.
• Capitalization and spaces matter. The passphrase is case-sensitive. A passphrase of Bitcoin2024 and bitcoin2024 produce different wallets.
• Start simple. For most beginners, a passphrase adds meaningful security but also adds meaningful risk of self-inflicted loss. If you choose to use one, keep it memorable and back it up carefully.

Many experienced Bitcoin holders use a passphrase as a standard part of their security setup. It is one of the most practical ways to add a second factor to cold storage without relying on any third-party service. That said, it is entirely optional. You can complete the setup and use the Coldcard effectively without one.

Connecting to Sparrow Wallet

Sparrow Wallet is a free, open-source Bitcoin wallet for Windows, macOS, and Linux. It provides a full-featured interface for managing your Coldcard accounts, viewing your balance, building transactions, and broadcasting them to the network. You can connect Sparrow to your own Bitcoin node for maximum privacy, or use a public server if you are just getting started.

Exporting the Wallet File via MicroSD

The cleanest way to connect the Coldcard to Sparrow is through the MicroSD card, which avoids any USB data connection between the two devices.

1. Insert your formatted MicroSD card into the Coldcard.
2. From the main menu, go to Advanced, then MicroSD Card, then Export Wallet.
3. Select Sparrow from the list of wallet software options. The Coldcard will write a JSON file to the SD card.
4. Remove the SD card and insert it into your computer.
5. Open Sparrow Wallet and go to File, then New Wallet. Give the wallet a name.
6. Select Airgapped Hardware Wallet as the script type, then click Import File and select the JSON file from the SD card.
7. Sparrow will import your public keys and display your wallet. You will be able to see your Bitcoin addresses and any balance associated with them.

At this point, Sparrow knows your public keys but not your private keys. You can receive bitcoin by sharing your addresses, and you can build transactions in Sparrow, but the Coldcard must sign any transaction before it can be broadcast. Your private keys never leave the device.

If you are still deciding whether the Coldcard is the right choice for you, it is worth comparing it to alternatives. Our Ledger vs. Trezor comparison covers two other popular options, and the Trezor Safe 5 review goes into detail on a device with a more beginner-friendly interface.

Sending Bitcoin with Air-Gapped Signing

One of the defining features of the Coldcard Mk4 is its ability to sign transactions without ever connecting to a computer via USB data. This air-gapped workflow uses the MicroSD card to pass an unsigned transaction from Sparrow to the Coldcard and return the signed transaction back to Sparrow for broadcasting.

Step-by-Step Transaction Signing

1. Build the transaction in Sparrow. Enter the recipient address, the amount you want to send, and set your fee rate. Click Create Transaction, then Finalize Transaction for Signing.
2. Save the PSBT file to the SD card. In Sparrow, click Save Transaction and save the partially signed Bitcoin transaction (PSBT) file to your MicroSD card.
3. Insert the SD card into the Coldcard. From the main menu, go to Ready to Sign. The Coldcard will detect the PSBT file on the card.
4. Review the transaction on the Coldcard screen. The device will display the recipient address, the amount, and the fee. Verify these details carefully. This is your last line of defense against address substitution attacks, where malware on your computer replaces the recipient address with an attacker's address.
5. Confirm and sign. If the details are correct, press the checkmark to sign. The Coldcard writes the signed transaction back to the SD card.
6. Broadcast from Sparrow. Remove the SD card, insert it into your computer, and in Sparrow go to Load Transaction. Select the signed file. Click Broadcast Transaction to send it to the Bitcoin network.

This workflow keeps your private keys completely isolated from any internet-connected device at every step. Even if your computer is compromised, the attacker cannot extract your keys because they were never present on the computer.

Understanding why this matters requires some context about how Bitcoin transactions work and why self-custody is important. If you are still building that foundation, our articles on what is Bitcoin and how to start stacking sats provide useful background.

Security Tips and Best Practices

Setting up the Coldcard correctly is only part of securing your bitcoin. The way you store your backups, handle your device, and manage your operational habits over time matters just as much as the initial configuration.

Seed Phrase Storage

• Never store your seed phrase digitally. No cloud storage, no photos, no password managers, no email drafts.
• Keep your seed phrase backup and your Coldcard device in separate physical locations. If both are in the same place and that location is compromised, you lose everything.
• Consider a metal backup for long-term durability. Paper can be destroyed by fire, flood, or simple deterioration over years.

PIN and Passphrase Hygiene

• Use a PIN that is not obvious but that you will remember. Losing your PIN does not immediately mean losing your bitcoin, because you can restore from your seed phrase, but it is an inconvenience you want to avoid.
• If you use a BIP39 passphrase, back it up with the same rigor as your seed phrase and store it separately.
• Verify your anti-phishing words every time you log in. If they change, treat the device as potentially compromised.

Firmware Updates

Coinkite releases firmware updates periodically to address security issues and add features. You can verify and install firmware updates via the MicroSD card without connecting to a computer. Check the Coinkite website for the latest release and always verify the firmware signature before installing.

Regular Verification

Every six months or so, verify that you can still access your wallet by entering your PIN and confirming your seed phrase backup is intact and readable. Do not wait until you need to make a transaction to discover that your backup is damaged or that you have forgotten your passphrase.

These habits apply regardless of which hardware wallet you use. If you are also thinking about how to build your Bitcoin holdings over time in a disciplined way, our guide on Bitcoin dollar-cost averaging covers a practical approach to accumulation that pairs well with proper cold storage.

Final Thoughts

The Coldcard Mk4 is not the most approachable hardware wallet for someone who wants to get set up in five minutes. But for a Bitcoin holder who wants to understand their security model and have full control over their keys, it is one of the most capable devices available. The air-gapped signing workflow, the dual secure elements, the open-source firmware, and the Bitcoin-only focus all reflect a consistent set of priorities: your keys stay on your device, and your device stays off the network.

The setup process described in this guide takes about an hour the first time. After that, using the Coldcard for routine transactions is straightforward once you are comfortable with the PSBT workflow in Sparrow. Most holders do not move their cold storage funds frequently, so the slightly longer signing process is a reasonable trade for the security properties it provides.

If you are coming from an exchange and moving to self-custody for the first time, the Coldcard Mk4 is a solid choice, though you may also want to consider whether a simpler device like the Trezor Safe 5 better matches your current comfort level. There is no single right answer. What matters is that you move your bitcoin off exchanges and into a wallet where you control the keys.

Bitcoin has a fixed supply of 21 million coins, secured by proof-of-work consensus, with the block subsidy halving roughly every four years. That scarcity is only meaningful to you if you actually hold your own keys. A hardware wallet is how you do that. The Coldcard Mk4 is one of the best tools available for the job.

For more context on why self-custody matters and how it fits into a broader Bitcoin philosophy, see our article on what is hard money. And if you want to compare the Mk4 against the newer generation, our Coldcard Mk5 review covers what changed in the next version.