The aging population phenomenon is more and more increasing. In this context, the elderly's behavioral analysis through the Internet of Things technologies can help to prevent Mild Cognitive Impairment and frailty problems. In particular, since movements and body motility are good indicators of behavioral changes, this work aims to define a reliable system for controlling the position and the body motility of the elderly in unobtrusive, low-cost and low-power way. The system represents the basis of a complete architecture for behavioral analysis and risk detection developed within the City4Age project, funded by the Horizon 2020 Programme of the European Commission.