John Ternus, Apple hardware engineering chief recently spoke with TechCrunch about the ‘parts pairing’ process for its repair program.

Apple’s parts pairing was criticized before by iFixit, claiming that Apple is blocking third-party parts from working. Ternus said that there have been a lot of negative connotations about it and that Apple does not block the parts from working. The Apple chief explained that they will need to authenticate that it’s a real biometric device and that it has not been tampered with, and calibration being the other reason.

One exception is Touch ID and Face ID, which will not work for security reasons. Ternus mentioned that the two components are critical to security due to having access to information. Apple believes that there’s no way to validate performance on third-party biometrics. The iPhone user gets an alert if the part is not genuine and Apple will be expanding the ‘Parts and Service History’ this year.