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TL;DR — A health check (verifying a key is accessible and functional) for a Coldcard uses MicroSD card signing because the Coldcard is airgapped (communicates via MicroSD card only, never USB). You initiate the health check in the Casa app, download a file to your computer, copy it to a MicroSD card, sign it on the Coldcard, then copy the signed file back to your computer and upload it. The whole process takes a few minutes. You will need your Coldcard, its PIN, a MicroSD card, a computer with a MicroSD card reader, and Chrome browser.
After adding your Coldcard to the Casa app, you can use it to perform a health check on the device. Please note that you will need to finish adding all the keys to your vault before you can perform a health check.
If you have not added your Coldcard to Casa yet, please see our article Adding Coldcard to your Casa vault.
If you want to learn how to sign a transaction with Coldcard, see Signing a Transaction with Coldcard.
When performing a health check, you will need:
- Coldcard device
- A laptop or desktop computer (mobile phone is not recommended)
- MicroSD card
- MicroSD card adapter (if your computer does not have a microSD card slot)
First, initiate the health check from within the Casa app by tapping the hardware device key icon and selecting "Perform Health Check."
Next, check your email inbox for an email from Casa with a link. Clicking that link will initiate the health check process.
Physically insert your MicroSD card into your computer (you may need an adapter for this step).
When you click the link, you’ll be prompted to download a .txt file onto your computer. Once the file is downloaded, drag and drop the file onto the Coldcard’s MicroSD card.
Next, take the MicroSD card out of your computer and insert it into your Coldcard.
When your Coldcard is powered up and unlocked with your PIN, navigate to:
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For MK3: Advanced > MicroSD Card > Sign Text File
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For MK4: Advanced/Tools > File Management > Sign Text File
Click "OK" to export the signed text file to the MicroSD card.
Now that the signed health check file is copied to the MicroSD card, you’re ready to transfer the file back to your computer to complete the Health Check verification process.
Remove the MicroSD card from the Coldcard and insert it into your computer.
Back in your web browser, click "Continue, I'm ready," then "Continue," then drag and drop the new file with a name that ends in "signed.txt" into the window when prompted.
If the signature is successfully verified, you'll see a success message and you're done! If you see an error then you may have added the wrong file or you may be using a device that is not a part of your current vault. Reach out to us at help@team.casa and we'll help you figure out what went wrong!
What to do if the health check fails
If the health check returns an error, try these steps before contacting support:
- Confirm you are using the correct Coldcard — the device that is part of your current vault, not a different Coldcard or a device marked for replacement during a key rotation (replacing one key in the vault with a new one).
- Make sure "Trust PSBT" is enabled on your Coldcard: navigate to Settings → Multisig Wallets → Trust PSBT? and select "Trust PSBT."
- Verify your Coldcard firmware is at or above the minimum recommended version. See: Supported platforms and hardware device firmware.
- Ensure you are dragging the correct file — the one ending in
-signed.txt— back into the browser window. - Try using Chrome browser if you are not already. Other browsers may cause issues.
For more troubleshooting steps, see: Coldcard troubleshooting.
Still having trouble?
If you have tried the steps above and the health check still fails:
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Standard members: email help@team.casa with a description of the error message you are seeing and which step you are on.
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Premium and Private Client members: reach out to your dedicated Client Advisor directly.