Abstract: A sensor assembly and sensing method is provided for proximity detection for assessing an attachment state of a sensing probe with respect to a subject. A probe is coupled to an electronic probe controller. The probe includes a proximity sensor having a passive energy storing circuit element, and a biological sensor receptacle configured to receive a biological sensor for sensing a biological characteristic of an object. The electronic probe controller excites a circuit network incorporating the proximity sensor with an excitation signal and determines a characteristic of the circuit network that is excited by the excitation signal. The electronic probe controller further generates a proximity indication indicating whether the probe is attached to the object based on the characteristic of the circuit network.