COLDCARD is a Bitcoin-only, non-custodial hardware wallet (the wallet’s website refers to it as a Bitcoin signing device) designed to keep your private keys online while retaining the ability to transact via Partially Signed Bitcoin Transactions (PSBT). 

A PSBT is like a filled-out check that you haven’t signed yet. Your wallet deciphers who you’re paying and how much, as well as the transaction fee, and saves that info as a PSBT, otherwise known as a partially signed transaction. You move that file to COLDCARD via microSD, verify these details on COLDCARD’s screen, and approve the transaction via another signature.

COLDCARD signs the transaction internally and returns it to the microSD, ready to broadcast to the Bitcoin blockchain. Your private key never leaves the wallet, while the multi-signature approach brings with increased security. 

COLDCARD Key Points

• Bitcoin-only focus: Bitcoin focus means fewer attack avenues.

• Air-gapped workflows: Partially Signed Bitcoin Transactions over microSD, QR code, and near-field communication (NFC), though USB and MicroSD are optional.

• Defensive stack: Dual secure elements, anti-phishing words, and physical lights.

• Backups and recovery: 24-word seed phrase, 

• Broad compatibility: Pairs well with wallets like Sparrow or Electrum.

COLDCARD Functions and Services

COLDCARD’s got a full focus on Bitcoin. If you want Ether (ETH), Solana (SOL), or non-fungible token (NFT) support, COLDCARD deliberately says no. That’s a feature. The vision: keep your long-term savings on COLDCARD, while a separate hot wallet holds your altcoin “play money.”

Here’s how COLDCARD functions:

Dual Secure Element

Modern COLDCARD wallets store your 24-word Bitcoin Improvement Protocol (BIP)-39 seed in two secure chip elements from different vendors. An attacker would need access to both chips and the wallet’s main microcontroller to steal your assets. This is far more difficult than compromising a single chip.

Physical Tamper Checks 

Upon booting your wallet, the device verifies its signed firmware and will flash a physical light upon completion. Green for genuine, red for caution. These LEDs are hardwired to your wallet’s secure element, meaning that no form of malware can fake a green light. If you power on the wallet after being away for some time and see a red light, do not enter your PIN.

Anti-Phishing Words

Anti-phishing words split your PIN into two halves. After entering your PIN’s first half, COLDCARD will show two secret words that are unique to your device. If you don’t recognize these words, your device has been tampered with. Do not finish your PIN.

Air-Gapped Operation

You can run your COLDCARD off a wall adapter or a battery pack rather than connecting it to an online device like your PC, keeping your seed phrases offline and inaccessible to any hackers. From there, you can export a light “skeleton wallet” to another wallet for trading via microSD. This is called “air-gapping” because it doesn’t expose your seed phrase to the internet.

Encrypted microSD Backups

Outside of writing down your 24-word seed phrase, COLDCARD can create an industry-standard AES-256 encrypted backup of your seed phrase and wallet settings on microSD, protected by a 12-word backup password. 

On and Off-Ramp Capabilities of COLDCARD

Unlike many of its contemporaries, COLDCARD doesn’t natively support buying or selling crypto. 

Instead, you purchase Bitcoin via an exchange or a broker and withdraw it to your COLDCARD address, which the platform recommends doing via MicroSD cards and a private wallet like Sparrow.

Is COLDCARD Safe to Use in 2025?

COLDCARD is built knowing that attackers are smart. With dual secure elements, a signed firmware boot, anti-phishing words, physical caution lights, and support for fully air-gapped operation, you hold your seed phrase, you control your keys, and you’re responsible for your security. 

Fully offline operation is about as safe as you can get when it comes to Bitcoin holdings, so understanding how to properly operate it ensures that COLDCARD is safe to use in 2025.

COLDCARD FAQs

Does COLDCARD work with Lightning Network?

Not directly. Think of COLDCARD as your vault (long-term storage). You can move small amounts from your vault to a spending wallet (like a mobile/Lightning wallet) whenever you need to pay. It’s more cumbersome than a traditional wallet, but more secure.

Is it safe to travel with COLDCARD through airport security?

Yes. X-ray scanners and metal detectors won’t “erase” your wallet. When travelling, you can even activate a Single Signer Spending Policy (SSSP) to activate limited features, preventing others from gaining access to your wallet.

Is COLDCARD’s software open for people to review?

Yes, you can read the project’s code on GitHub. That said, COLDCARD only runs officially signed firmware, which prevents malicious hardware installations pretending to be an update.

Can I use COLDCARD with other brands in a multi-sig method?

Yes. Wallets like Sparrow let you mix different hardware wallets in the same setup. If one brand has a problem or gets lost, the others still keep your Bitcoin safe.