The in vitro simulation of organs resolves the accuracy, ethical, and cost challenges accompanying in vivo experiments. Organoids and organs-on-chips have been developed to model the in vitro, real-time biological and physiological features of organs. Numerous studies have deployed these systems to assess the in vitro, real-time responses of an organ to external stimuli. Particularly, organs-on-chips can be most efficiently employed in pharmaceutical drug development to predict the responses of organs before approving such drugs. Furthermore, multi-organ-on-a-chip systems facilitate the close representations of the in vivo environment. In this review, we discuss the biosensing technology that facilitates the in situ, real-time measurements of organ responses as readouts on organ-on-a-chip systems, including multi-organ models. Notably, a human-on-a-chip system integrated with automated multi-sensing will be established by further advancing the development of chips, as well as their assessment techniques.