There is ongoing discussion about transforming online questionnaires into an appropriate mobile device design in order to avoid mode-effects and safeguard data quality. However, a crucial point in implementing online questionnaires is often neglected or less discussed: The dropout rates of potential participants due to problems in accessing the online instrument caused by a faulty or inconvenient login process. In our qualitative study, concrete evidence on the design of an easy login on Smartphones could be iteratively developed to meet users’ requirements. Results suggest using catchy passwords, displaying passwords rather than fading them and implementing proportional fonts rather than non-proportional. Moreover, we analysed the duration of the login process, the layouts of different keyboards, the design of input fields, the layout of the login information in the invitation letter and the subjective ratings of lead probands on subjective efforts and security issues. In the end, we developed a combination of login design elements, which better suit the user’s perspective. However, further investigation on data security requirement is needed before a new design can be implemented.