A system, device and method monitoring whether a core temperature of a warm-blooded pet animal is within a normal range for the pet animal comprises a sensing assembly including (i) a skin temperature sensor positioned such that a sensing surface of the skin temperature sensor faces the animal, the skin temperature sensor configured to produce a skin temperature output, (ii) an ambient temperature sensor spaced away from the animal and configured to produce an ambient temperature output, and (iii) an accelerometer for sensing an acceleration of the pet animal and producing an acceleration output and a processor for receiving the outputs, calculating an activity level from the acceleration data and determining whether the core temperature of the pet animal is within the normal range based on a pre-defined function relating the skin temperature TS, the ambient temperature TA, and the activity level of the pet animal.
