Comprehensive, continuous quantitative monitoring of intricately orchestrated physiological processes and behavioral states in living organisms provides an important tool for elucidating the function of neural circuits under healthy and diseased conditions, for defining the effects of potential drugs and treatments, and for monitoring disease progression and recovery. Here, we report a wireless, battery-free implantable device and a set of associated algorithms that enables continuous, multiparametric physio-behavioral monitoring in freely behaving small animals and interacting groups, through mechano-acoustic sensing of body processes. The device captures a diverse spectrum of physiological and behavioral features, parsed by algorithms to yield heart rate, respiratory rate, physical activity, body temperature, and behavioral states (resting, eating, walking, rearing, grooming, and digging), without measurable constraints on locomotion or other natural activities. Demonstrations in pharmacological, running wheel, forced swim, shock grid, resident-intruder, and witness defeat tests illustrate a broad set of representative applications relevant to studies in neuroscience and biomedicine. Chronic, continuous monitoring in a freely behaving mouse for 17 days reveals circadian effects on physio-behavioral characteristics, as a demonstration of the reliability and stability of operation necessary for research across various temporal scales. Integration into freely moving, small animal models implanted with a separate wireless device provides an opportunity to monitor physiological changes during optogenetic manipulation of neural circuits.