Embodiments of the present invention provide a system and method for authorizing the use of a biometric transaction card. Specifically, embodiments of the present invention provide a biometric card having a biometric sensor to determine whether the biometric information (fingerprint) is from human skin. In a typical embodiment, the cardholder approaches a magnetic reader with the card. The user places his/her finger on the SpO2 sensor of the card. The sensor estimates the SpO2 level. Card authorization is based, in part, on the estimated SpO2 level.