A detector and a method of its use with a guidewire to reduce the incidence of guidewires accidently being left inside patients during the placement of central venous (and other) catheters. In particular, an electronic detector detects whether a catheter has been placed over a guidewire and whether the guidewire has been removed thereafter. In addition, the distance the guidewire has progressed out the patient side of the detector housing which will correspond to the length of guidewire actually inside the patient and any time may be provided.
