Cold storage is removing your cryptocurrency keys from your wallet and storing them somewhere that is not connected to the network or internet. Additionally, cold storage methods shouldn't have the ability to communicate with any other electronic device unless it is physically plugged into that device when you're accessing your keys.
Cold storage became a concern early on in cryptocurrency's development because of concerns over key theft by hackers. Originally, it consisted of writing down the keys on a piece of paper and removing them from the wallet. Cold storage has since advanced because users have billions of dollars worth of cryptocurrency.
Placing your hardware wallet in your safe is secure, but it isn't considered deep cold storage because it is easy for you to access. Deep cold storage is any method that is very inconvenient and requires time and effort to retrieve your keys. This could be anything from placing your hardware wallet in a waterproof container and burying it six feet down in your garden to using a third-party service that stores your cryptocurrency keys in a vault that requires multiple steps to access.
Hackers would encounter great difficulty in attempting to steal client assets. This is because our vaults uses a “specific” technology to secure digital assets.