The BETTER4U project (Preventing obesity through Biologically and bEhaviorally Tailored inTERventions for you) is funded by the European Union (EU) and involves an international consortium consisting of 28 partners across Europe, Israel, and Australia. The project started in November 2023 and will run until October 2027. The main aim of BETTER4U is to improve weight management through a tailor-made intervention, the BETTER4ALL personalized intervention, using modern monitoring tools and artificial intelligence (AI), including machine learning (ML) practices. In the context of the BETTER4U project, the present Pilot Study aims to a) evaluate the usability, feasibility and acceptability of the BETTER4U mobile application (BETTER4U App) and Intervention Platform that will be used to monitor and collect data from participants in the BETTER4ALL personalized intervention (randomized controlled trial; RCT) and b) collect data to evaluate and improve the BETTER4U causal AI models for the prevention of weight gain, before deploying them at large scale, as well as test and identify the optimal ways of delivering the AI-based interventions to the participants. The study will be conducted in seven sites in Cyprus, France, Greece, Poland, Portugal, Spain, and Sweden. The BETTER4All Pilot Study will be a longitudinal, correlational, observational study, including a total of n=490 participants, equally distributed among the seven sites (i.e. n=70 per site). Specifically, n=60 (± 3-5) general population participants (henceforth: end-users of the wearables and the BETTER4U App) and n=10 (± 3-5) healthcare or other types of providers (henceforth: potential implementers of the BETTER4U intervention) will constitute each site's sample. The study will involve the following two components: a) the administration of the wearables (smartwatches) to the end-users and their registration to and training on the BETTER4U App, to be used for a total duration of three weeks (21 days). During this period, their lifestyle behaviours (i.e. BETTER4U Core Behavioural Indicators - BCBIs, such as eating occasions, physical activity, sedentary time, sleep etc.) and living environment indicators - LEIs; (e.g. access to parks in your area, distance from your home to your work place etc.) will be recorded daily, either in an automated way via the wearables or self-reported by the end-users through the App; and b) the registration to and training on the BETTER4U Intervention Platform of the implementers for a total duration of one week (7 days), during which they will be asked to test the platform's functionalities using synthetic data. The implementers will also be provided with the wearables and the App (similarly to the end-users) for one week only to allow collection of additional data that will help verify the accuracy of the algorithms in the gathered data from the wearables/monitoring tools regarding BCBIs and LEIs. Overall, the outcomes and the findings of the Pilot Study will be used to further refine, optimize, and adjust the tools for the BETTER4ALL RCT, according to the feedback received by both end-users' and implementers' perspectives.