The present teaching relates to method, system, medium, and implementations for detecting a target object via a security post. A plurality of sections are arranged in a vertical direction. Each section is designated to detect the target object in a vertical range by receiving information related to magnetic field from one or more sensors, analyzing the sensed information to extract features characterizing the magnetic field variations in the corresponding vertical range, and determining whether the target object is present in the vertical range based on the extracted features. When the target object is detected by a section, an alarm associated with the section is triggered to indicate the detection. An overall detection result is determined based on the detection result from each of the sections and is displayed on a display screen.