Smartphones have become increasingly popular among every segment of the population. Caregivers do not want to miss out on this evolution and express interest in using mobile devices to perform their everyday care. This tendency has been well understood by many software providers who have produced many medical applications for smartphones. Before going a step further and developing tools to manage Clinical Information System data on handheld devices, it is wise to ask ourselves whether these new tools are well adapted to the healthcare environment. Indeed, some studies have raised concerns regarding the efficiency of these handheld devices to input medical data, especially with the induced errors. In this paper, we look to adopt a rigorous approach to acquire evidence about these concerns through a prospective study. In order to get this evidence, the study compares several input interfaces in the context of recording vital signs on mobile devices. We would like to discover not only which interface is the most efficient, but also which one is the least prone to errors.