Hardware wallets are also good

1
Use several old phones to save, store in different places, the wallet is generated on the old phone 【The phone is always offline】
2
Never connect to the internet, go to Xianyu to buy a phone that cannot connect to the internet, use Bluetooth to transfer the software!
3
Save QR codes and mnemonic phrases as screenshots in the old phone, then use Bluetooth to send them to other old phones separately
4
When importing the mnemonic phrase into the connected phone, first turn off all networks, and only turn on the network after the import is successful! This is to prevent any spying software on your phone!