The security door is a detection device that detects the presence or absence of metal objects, such as firearms, control tools, and the like. When the inspected person passes through the security door and the metal carried on the person's body exceeds the parameter value preset according to the weight, quantity or shape, the security door immediately alarms and displays the location of the metal causing the alarm, so that the security personnel can promptly Discover the metal objects that the person carried with him.