Multi-sensor tags capable of collecting fine-scale acoustic, diving, kinematic, and electrocardiogram data have given scientists insights into many aspects of cetacean ecology and physiology. In this talk I discuss a new multi-sensor tag hardware and software platform, FaunaTag and tagOS, I have been developing and testing over the past two years. This non-invasive tag features a custom-designed biomedical optics sensor package. specifically a multi-wavelength, near-infrared, spatially-resolved diffuse reflectance sensor module, optimized for measurement of cetacean physiological signals through highly-pigmented epidermal tissue. Coupled with electro-cardiogram (ECG), depth, and kinematic sensors, the FaunaTag is expected to provide new insights into cetacean heart rate variability, tissue perfusion, and, potentially, blood oxygen saturation, with a goal of studying cetacean ecophysiology in both captive and wild contexts. I will also discuss work that is underway to adapt the tag platform for use in terrestrial physiology and ecology research.