What does airgapped mean?

TL;DR — An airgapped hardware device is one that communicates via QR code or MicroSD card only, never through USB, Wi-Fi, Bluetooth, or any other wired or wireless connection. Because the device never connects directly to your computer or phone, it eliminates an entire category of remote attack. Casa supports three airgapped device families: Coldcard (MicroSD card), Passport (QR code), and Keystone Pro (QR code). All three are compatible with Casa BTC vaults only.

What "air-gapped" means

An airgapped device is physically isolated from the internet and from any other device. There is a literal "air gap" between the hardware device and the outside world — no cable, no wireless signal, and no network connection of any kind. The device generates and stores your private key entirely on its own hardware, and that key never leaves the device.

When you need to perform a signing (the act of a key authorizing a transaction) or a health check (verifying a key is accessible and functional), data is transferred between the Casa app and the airgapped device using one of two methods:

QR codes — The Casa app displays a QR code on your phone or computer screen. The airgapped device scans it with its built-in camera. After signing, the device displays a new QR code on its own screen, which you scan back using your phone. No data travels over a network at any point.
MicroSD card — The Casa app saves a transaction file to your computer. You copy that file onto a MicroSD card, physically insert the card into the airgapped device, sign the transaction on the device, then move the card back to your computer to complete the process.

In both cases, the device itself never touches the internet. The only data that moves between the device and your computer is the specific transaction being signed, nothing more.

Why air-gapping adds security

Most cyberattacks require some kind of network connection to reach a device. Malware, phishing tools, and remote exploits all depend on a path between the attacker and the target, usually the internet, a USB cable, or a wireless signal. An air-gapped device removes all of these paths. Even if your computer or phone were compromised, an attacker would have no way to reach the airgapped device or extract its private key remotely.

This is especially valuable in a Casa vault, which uses multisig (requiring more than one key to authorize a transaction). If one of your keys is held on an air-gapped device in a separate physical location, the security of that key does not depend on the security of your computer, your phone, or your home network. An attacker would need physical access to the device itself, and even then, they would still need additional keys from your signing quorum (the minimum number of keys required to send bitcoin) to move any funds.

Which Casa-compatible devices are airgapped?

Casa supports three airgapped hardware device families. All three are compatible with Casa BTC vaults only, they cannot be used for ETH vaults.

Device	Communication method	Notes
Coldcard (Mk4, Mk5, Q)	MicroSD card	Transaction files are transferred via MicroSD card between your computer and the Coldcard. The Coldcard Q model has a QR code scanner, but QR code signing is not supported with Casa — only MicroSD card signing works.
Passport (V1 / Batch 2)	QR code	Uses the device's built-in camera to scan QR codes from the Casa app. The device displays a signed QR code on its screen for your phone to scan back. Passport Batch 2 has been renamed to Passport Core.
Keystone Pro	QR code (primary) or MicroSD card	QR code signing is the recommended method. MicroSD card signing is also available as an alternative for advanced users. Note: only the Keystone Pro is compatible with Casa — the newer Keystone 3 Pro is not supported.

Trezor, Ledger, and YubiKey devices connect via USB and are not airgapped. They are still secure choices for a Casa vault, USB-connected devices simply use a different approach to protecting your key. For a full comparison, see: Which hardware device should I use with Casa?

What you need for airgapped signing with Casa

The requirements depend on which device you are using:

For Coldcard (MicroSD card signing)

A Coldcard device (Mk4, Mk5, or Q) with current firmware
A MicroSD card (included with most Coldcard purchases)
A computer with a MicroSD card reader (you may need a USB adapter)
Chrome browser on your computer
The Casa app on your phone

For Passport (QR code signing)

A Passport device (V1 or Batch 2 / Passport Core) with current firmware
The Casa app on your phone — QR codes are displayed in the app and scanned with the Passport's built-in camera
No computer required for QR code signing

For Keystone Pro (QR code signing)

A Keystone Pro device with current firmware
The Casa app on your phone — QR codes are displayed in the app and scanned with the Keystone's built-in camera
No computer required for QR code signing (a computer is needed only if you choose MicroSD card signing as an alternative)

Common questions about airgapped devices

Is an airgapped device harder to use than a USB device?

QR code signing is very straightforward — you scan a code, confirm on the device, and scan a code back. Most members find it takes only slightly longer than USB signing. MicroSD card signing involves a few extra steps (copying a file, moving the card), but it becomes routine after the first time. Casa provides step-by-step guides for every device.

Can I use an airgapped device for my ETH vault?

No. Coldcard, Passport, and Keystone Pro are all compatible with Casa BTC vaults only. If you need a hardware device for your ETH vault, choose a Trezor or Ledger device.

Do I still need a seed phrase with an airgapped device?

Yes — Coldcard, Passport, and Keystone Pro all generate a seed phrase (a 12- or 24-word backup of the device's private key) during initial setup. However, in a Casa vault that uses multisig, keeping a copy of the seed phrase is optional for a 3-key vault and recommended for only one device in a 5-key vault, because any single lost key can be replaced through a key rotation (replacing one key in the vault with a new one) as long as the remaining keys in your signing quorum are intact.

Is airgapped more secure than USB?

Airgapping removes one category of risk — remote attacks that travel over a cable or wireless connection. However, USB-connected devices like Trezor and Ledger are also designed with strong security protections, including secure elements and PIN protection. In the context of a Casa multisig vault — where your keys are distributed across multiple devices in separate locations — both approaches provide strong security. The choice depends on your preferences and comfort level.

Need help with your airgapped device?

If you are having trouble setting up or signing with an airgapped device, or if you are not sure whether airgapped signing is right for your setup:

Standard members: email help@team.casa with a description of your device and the issue you are experiencing.
Premium and Private Client members: reach out to your dedicated Client Advisor directly.