For purchases made from your Apple Wallet, Apple Pay is very secure and requires authentication using either Face ID, Touch ID or your device passcode for every transaction. For more information on Apple Pay security and privacy click here.
For purchases made from your Google Wallet, GPay is very secure and will require that you unlock your device using your chosen authentication method for purchases over $50. You will only be able to complete a limited number of transactions under $50 with a locked screen before your device will require unlocking to complete further purchases. For more information on GPay security and privacy click here.