Mobile devices are becoming more and more important for services offered either directly to individuals, or indirectly as part of a therapeutic or rehabilitation procedure. Representing the work of the EFMI WG “Personal Portable Devices”, this paper offers an introduction to some of the most important technical and privacy-related challenges that arise when introducing mobile sensor or actuator devices (and networks) into health care, wellness, and fitness processes in order to exploit their capability to collect, record and process personal health data. Data processing can be viewed in three classes of application, namely processes for recommendations, decision support and decision making in personalized health and wellbeing service provision. This paper therefore briefly addresses aspects such as the Medical Device Directive for certifying devices in that respect. But regardless whether being MDD-compliant or not, each class of devices may have its own benefits and weaknesses in terms of enabling health-related personalized decisions.