An apparatus for detecting a surgical implement in human or animal tissue has means for defining a transmitting zone encompassing a surgical wound in the tissue. A battery powered marker is secured to a surgical implement positioned within the wound. Field generating means are provided for generating within the transmitting zone an electromagnetic field having a predetermined frequency band. A signal generating means generates a signal having a predetermined frequency band. The signal generating means is operative to cause the field generating means to generate the electromagnetic field, providing the marker with signal identity. A detecting means having an antenna located within the transmitting zone of the marker detects the marker signal irrespective of the marker's orientation therewithin.