Generally, when talking about privacy protection, most Smartphone users pay attention to the safety of SMS, emails, contact lists, calling histories, location information and private files. Since they are mobile and used as everyday gadgets, they are susceptible to get lost or stolen. Hence, access control mechanisms such as user authentication are required to prevent the data from being accessed by an attacker. However, commonly used authentication mechanisms like PINs, passwords and android unlock patterns suffer from the same weakness: they are all vulnerable against different kinds of attacks, most notably shoulder-surfing.