Monitoring physiological and behavioral parameters of laboratory rodents is fundamental for biomedical research, yet conventional techniques often rely on invasive sensors or frequent handling that can induce stress and compromise data fidelity. To address these limitations, this paper presents a contactless and non-invasive in-vivo monitoring system based on a low-power 60 GHz frequency-modulated continuous wave (FMCW) radar. The proposed system enables simultaneous detection of rodent activity and vital signs directly within home-cage environments, eliminating the need for implants, electrodes, or human intervention. The hardware platform leverages a compact Infineon BGT60 series radar sensor, optimized for low power consumption and continuous operation. We investigate sensor placement strategies and design a complete signal processing pipeline, including range bin selection, phase extraction, and frequency-domain estimation tailored to rodent vital signs. The system achieves 3 cm and 0.1 m/s sensitivity for motion and activity detection, while allowing discrimination of micro-movements associated with cardiopulmonary activity with a 2 um distance resolution. Experimental validation with two rodents in realistic in-vivo cages demonstrates that the radar can track animal position and extract respiration rates with 2 bpm accuracy. By minimizing stress and disturbance, this work improves both animal welfare and the reliability of physiological measurements, offering a refined alternative to traditional monitoring methods. This work represents the first demonstration of continuous radar-based vital sign monitoring in freely moving rodents within group-housed cages. The proposed approach lays the foundation for scalable, automated, and ethical monitoring solutions in preclinical and translational research.