ABSTRACT The primary mission of animal research facilities is assuring the health and well-being of its animals for ensuring the integrity, reliability, and reproducibility of research results obtained by humanely using animals. To achieve this, facilities deploy a variety of methods, including careful control of animal protocols, thoughtful engineering of facilities, and diligent screening for infectious agents. Despite best efforts, these methods cannot comprehensively protect animals from all possible vulnerabilities; therefore, robust monitoring tools are needed to alert caretakers to problems in their facilities as highlighted in the NIH FOA PAR-19-266. The proposed work will develop a new tool that monitors the health and well being of mice in animal facilities by embedding a genetic reporting system into sentinel mice. Cellgorithmics, has invented new CRISPR-Cas9-based technologies that enable time-resolved recording of physiological events to be made in the genomic DNA of sentinel mice. By expressing the system in the mouse intestine, the recorded events are effectively “read” by rapid and inexpensive sequencing of fecal DNA collected from sentinel mice. In two Aims, the proposal seeks to 1) build a base system in mice that can be combined with triggering systems to make sentinels, and 2) calibrate the response of the base system using doxycycline as a triggering event in a model sentinel. Completion of the proposed work in Phase I will provide the basis for the engineering of triggering systems in Phase II to monitor physiological stress responses, inflammation, and exposure to pathogens in new sentinel mice. This new tool will address critical unmet needs of animal facilities by providing a way of monitoring stress and health conditions that directly affect mice, but would otherwise go undetected.