A magnetic security marker of an article surveillance system is deactivated by first determining the status of the marker by exposing it to the interrogating field. If the marker is active, a deactivation field is applied to the marker. The marker is again interrogated using the interrogating field and, if an active marker is detected, an incrementally increased deactivation field is applied. The marker is continually interrogated and, as long as an active marker is detected, the intensity of the field is incrementally increased until the field reaches a level effecting deactivation.