A method of laser scanning a perimeter zone of a target site for the detection of potential threats comprises: scanning a pulsed laser beam across the perimeter zone; receiving echoes from the pulsed laser beam during the perimeter zone scan; deriving range data corresponding to the received echoes; determining position data of the received echoes in the perimeter zone; forming a scene image of a scan of the perimeter zone based on the range and position data of the received echoes thereof; repeating the steps of scanning, receiving, deriving, determining and forming for a plurality of perimeter zone scans to form scene images of each scan of the plurality; and comparing scene images of the plurality to detect a potential threat in the perimeter zone. In addition, a method of authenticating a potential threat detected in a perimeter zone of a target site comprises: detecting the potential threat and upon detection, interrogating the potential threat for a response by a wireless transmission; declaring the potential threat unauthorized if no response is transmitted wirelessly within a predetermined time interval from the interrogation; receiving the response, if transmitted, and determining if the response comprises a proper access code; and declaring the potential threat unauthorized if the received response is determined not to comprise the proper access code.