An implantable vessel filter having an integrated sensing capability for monitoring the condition of the vessel filter. In one variation, the vessel filter comprises a plurality of legs that would themselves perform as a sensor device for detecting distention, which would indicate the presence of a clot or thrombus therein. A passive electrical circuit may be implemented on the vessel filter to receive electromagnetic energy and transmit signals indicative of the condition of the implanted vessel filter. In another variation, a miniaturized sensor is adapted for measuring the strain and/or other physical parameters of the filter legs.