IN JULY, ONE BUG IN ONE COMPANY'S FIRMWARE EMPTIED THOUSANDS OF BITCOIN WALLETS. MOST PEOPLE USING THAT SAME DEVICE INSIDE A MULTISIG LOST NOTHING. That's the whole case for multisig. One seed phrase, one device and one company's code is a single point of failure. Multisig takes it away. Here's how it works, and how to set one up without getting it wrong. What it is A normal wallet has one key, and whoever has it can spend. A 2-of-3 multisig has three keys, and it takes any two to move a single sat. A thief with one key gets nothing. Lose one key and you can still get in with the other two. The rule is built into the Bitcoin address itself, so nobody can override it. What you need Three hardware wallets, ideally from three different makers, so one company's bug can only ever touch one of your keys. A metal backup for each seed phrase. And free software to tie them together. Sparrow is a popular choice on Bitcoin. Setting it up 1. Set up each hardware wallet on its own, with a brand new seed. Never type a seed phrase into a computer or a phone. 2. In Sparrow, create a new wallet, choose multi signature and set it to 2 of 3. Add each device as one of the keys. 3. Sparrow gives you a wallet file. Save it and print it. More on why below. 4. Send in a small amount. Then send it back out, signing with two of the devices. If that works, the setup works. 5. Now the step almost everyone skips. Delete the wallet from Sparrow and rebuild it from the wallet file. Check the first receive address matches. Only then move your real savings. The wallet file This is the part that catches people out. To rebuild a multisig you need two of the seeds and the wallet file. Lose the file and you'll need all three keys to put it back together, which defeats the point. The file can't spend anything, so keep a copy with each key. But it shows every address and your full balance, so treat it as private. Don't email it, don't upload it. Where to keep the keys Three places, one key in each. For example, one at home, one with family or at the office, and one in a safe deposit box. Each place gets the device, its seed backup and a copy of the wallet file. Someone who gets into any one place gets one key, and one key isn't enough. The mistakes that cost people 2-of-2. It sounds safer, but lose either key and the coins are gone for good. All three devices from the same maker. Two keys in the same house. One fire or one break-in takes both. Letting a company hold enough keys to sign. If a company holds one, it should only ever be one. Never testing a recovery until the day you actually need it. What it costs The software is free. The real cost is three hardware wallets and three metal backups. Each spend costs a little more in fees than a normal wallet, because the transaction carries more signatures. Your family If something happened to you tomorrow, could your family get in? Write them a short letter. Say it's a 2-of-3 multisig, where each key is, which software to use and who they can ask for help. Never put a seed phrase in that letter. When you need it It isn't a dollar amount. Ask yourself one question. Would losing this change your life? If the answer is yes, one key is carrying too much. Hold your keys. Plural.