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@ Cerebrum
2025-05-04 17:06:47COLDCARDS’s new Co-Sign feature lets you use a multisig (2 of N) wallet where the second key (policy key) lives inside the same COLDCARD and signs only when a transaction meets the rules you set-for example:
- Maximum amount per send (e.g. 500k Sats)
- Wait time between sends, (e.g 144 blocks = 1 day)
- Only send to approved addresses,
- Only send after you provide a 2FA code
If a payment follows the rules, COLDCARD automatically signs the transaction with 2 keys which makes it feel like a single-sig wallet.
Break a rule and the device only signs with 1 key, so nothing moves unless you sign the transaction with a separate off-site recovery key.
It’s the convenience of singlesig with the guard-rails of multisig.
Use Cases Unlocked
Below you will find an overview of usecases unlocked by this security enhancing feature for everyday bitcoiners, families, and small businesses.
1. Travel Lock-Down Mode
Before you leave, set the wait-time to match the duration of your trip—say 14 days—and cap each spend at 50k sats. If someone finds the COLDCARD while you’re away, they can take only one 50k-sat nibble and then must wait the full two weeks—long after you’re back—to try again. When you notice your device is gone you can quickly restore your wallet with your backup seeds (not in your house of course) and move all the funds to a new wallet.
2. Shared-Safety Wallet for Parents or Friends
Help your parents or friends setup a COLDCARD with Co-Sign, cap each spend at 500 000 sats and enforce a 7-day gap between transactions. Everyday spending sails through; anything larger waits for your co-signature from your key. A thief can’t steal more than the capped amount per week, and your parents retains full sovereignty—if you disappear, they still hold two backup seeds and can either withdraw slowly under the limits or import those seeds into another signer and move everything at once.
3. My First COLDCARD Wallet
Give your kid a COLDCARD, but whitelist only their own addresses and set a 100k sat ceiling. They learn self-custody, yet external spends still need you to co-sign.
4. Weekend-Only Spending Wallet
Cap each withdrawal (e.g., 500k sats) and require a 72-hour gap between sends. You can still top-up Lightning channels or pay bills weekly, but attackers that have access to your device + pin will not be able to drain it immediately.
5. DIY Business Treasury
Finance staff use the COLDCARD to pay routine invoices under 0.1 BTC. Anything larger needs the co-founder’s off-site backup key.
6. Donation / Grant Disbursement Wallet
Publish the deposit address publicly, but allow outgoing payments only to a fixed list of beneficiary addresses. Even if attackers get the device, they can’t redirect funds to themselves—the policy key refuses to sign.
7. Phoenix Lightning Wallet Top-Up
Add a Phoenix Lightning wallet on-chain deposit addresses to the whitelist. The COLDCARD will co-sign only when you’re refilling channels. This is off course not limited to Phoenix wallet and can be used for any Lightning Node.
8. Deep Cold-Storage Bridge
Whitelist one or more addresses from your bitcoin vault. Day-to-day you sweep hot-wallet incoming funds (From a webshop or lightning node) into the COLDCARD, then push funds onward to deep cold storage. If the device is compromised, coins can only land safely in the vault.
9. Company Treasury → Payroll Wallets
List each employee’s salary wallet on the whitelist (watch out for address re-use) and cap the amount per send. Routine payroll runs smoothly, while attackers or rogue insiders can’t reroute funds elsewhere.
10. Phone Spending-Wallet Refills
Whitelist only some deposit addresses of your mobile wallet and set a small per-send cap. You can top up anytime, but an attacker with the device and PIN can’t drain more than the refill limit—and only to your own phone.
I hope these usecase are helpfull and I'm curious to hear what other use cases you think are possible with this co-signing feature.
For deeper technical details on how Co-Sign works, refer to the official documentation on the Coldcard website. https://coldcard.com/docs/coldcard-cosigning/
You can also watch their Video https://www.youtube.com/watch?v=MjMPDUWWegw
coldcard #coinkite #bitcoin #selfcustody #multisig #mk4 #ccq
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