Smart Objects (SOs) are products that can exchange information about themselves and the environment due to IOT (Internet of Things) technologies. SOs use IOT technologies for increasing features of traditional objects by communicating and sharing knowledge with the environment. Few pilot applications are currently developed for preventing accidents at workplace. In this study, a preliminary analysis about potentialities of these technologies for preventing accidents at workplace. Next, a prototype solution designed to prevent injuries at semi-automatic assembly line systems is described in detail.