It's just an address check against a given Xpub. The signer and the wallet app are just cross referencing the same address list. Basically ensuring the keys on the signer are connected to the produced address. COLDCARD Q -Txn comes in, Copy it as QR -Scan the QR code with your COLDCARD Q. The device will show you the address and ask you to press 1 to verify ownership. -If the address is verified successfully, the COLDCARD will show "Verified Address" with details about the address. If the address cannot be found, the Q will show "Unknown Address". Very similar workflow for keystone as well.