Bitcoin vaults in the Casa app use an HD (hierarchical deterministic) key type, which generates a new address with each transaction that's made.
When sending funds, leftover amounts in UTXOs get returned to the sending wallet to a new address. This is known as a "change" address.
Some hardware devices, like Trezors, may ask you to confirm an additional "change" address when sending funds from the Casa app.
Is it safe to confirm the change address on the device?
It is normal for the device to show the funds being sent back to an address associated with your wallet and ask you to confirm.
If you would like to verify these addresses for yourself, we recommend creating a watch-only wallet for your Casa funds, which allows you to independently verify aspects of your wallet, such as the associated bitcoin addresses.
For more information on how change addresses work and why they are built into the bitcoin protocol, see https://en.bitcoin.it/wiki/Change
Why doesn't my ETH vault use change addresses?
Casa ETH vaults are a little different than Casa BTC vaults. In your ETH vault, you have a single ethereum address which is static (does not change), and is the only address associated with your vault.