The Internet of Things (IoT) have become significantly important in authentication mechanisms in which traditional authentication have shift to the biometric factors whereby biometric is said to offer more security and convenience to the users. The purpose of this paper is to provide an extensive review on biometric factors for smart home environments that are intended for security, comfort, healthcare, and energy saving. This paper also discusses the security authentication mechanisms, which are knowledge factor (password, PIN), ownership factor (ID card, passport), and inherent factor (fingerprint, iris, facial), known as biometric factors. Biometric factors can be used as authentications for smart home environments, which are more robust and reliable in terms of accuracy, convenience, and speed.