Abstract: An active system for tagging and detecting a surgical implement accidentally left within a patient after the completion of a surgical procedure. A miniature electrical oscillator is attached to each implement and actuated before surgery begins. The pulsed output of each oscillator is coupled to the body's internal fluids and tissue. Before the patient is sutured, a detector, located externally from the body, is employed to sense the pulses from any remaining implements. In the event such pulses are sensed, a sensory alert is actuated and corrective action taken.