Touch screens have become ubiquitous in the past few years, like for instance in smartphones and tablets. These devices are often the entry door to numerous information systems, hence having a secure and practical authentication mechanism is crucial. In this paper, we examine the complexity of different authentication methods specifically designed for such devices. We study the widely spread technology to authenticate a user using a Personal Identifier Number code (PIN code). Entering the code is a critical moment where there are several possibilities for an attacker to discover the secret. We consider the three attack models: a Bruteforce Attack (BA) model , a Smudge Attack (SA) model, and an Observation Attack (OA) model where the attacker sees the user logging in on his device. The aim of the intruder is to learn the secret code. Our goal is to propose alternative methods to enter a PIN code. We compare such different methods in terms of security. Some methods require more intentional resources than other, this is why we performed a psychological study on the different methods to evaluate the users' perception of the different methods and their usage.