Managing everyday wellness using sensors requires user buy-in and acceptance. The Unified Theory of Acceptance and Use of Technology (UTAUT) was used to measure at D-0 the acceptability (a priori), and at D-21 the acceptance of an ambulatory monitoring system under develop-ment, the SHERPAM system. Interviews with the participants revealed that they no longer viewed the system in the same way at the different stages of the study. The results of the qualitative analysis suggest that the time of the research led the participants to stop seeing themselves as potential future users and to take on the role of critical testers of the technology (which corresponds more to a user test). This role change led participants to question the usefulness of the technology, which affected their intention to use the technology in the future (5.30 vs. 4.24; t = 2.58 *). This research identified the reasons why it was crucial to have a fully functional device in the second phase (acceptance study). The results of this study suggest that it is inappropriate to undertake an acceptability study when the technology is under development. While the SHERPAM platform has been the subject of several user tests, none have been carried out in a situation of use. Thus, this study seems to suggest that the dysfunctions observed are more related to the absence of a development phase in the daily activity of the users. Thus, to ensure a good appropriation of the technology and to predict its use, the technology must not only be in perfect working order, but must also have been developed ac-cording to the daily activities of the individuals. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.