Several cold storage multisig solutions to prevent supply chain attacks: 1. Install Blue Wallet on 3 iPhones and set up multisig directly in Blue Wallet. For an extra layer, pair it with Sparrow multisig. 2. Use three different brands of hardware wallets (excluding Coldcard and Ledger) with Sparrow multisig. 3. A mix: two brands of hardware wallets + 1 iPhone with Blue Wallet. Set up multisig in Sparrow Wallet. The more secure, the more complex. Choosing a more complex solution also increases the risk of forgetting.