A ferromagnetic threat warning system utilizing two or more radio frequency transmitters or transceivers. A remote transmitter or transceiver is attached to each ferromagnetic threat that may enter the area to be protected. A master receiver or transceiver is mounted at each door controlling entry into the area to be protected. Communication between any master unit and one or more remote units generates an alarm when one or more threat objects approaches within a preselected distance of any master unit. Approach of a threat object within the preselected distance from a door can be detected when the strength of a radio signal between the remote unit associated with the threat object and the master unit near the door reaches a predetermined level. Generation of an alarm can be initiated at either the affected remote unit or the affected master unit. Generation of an alarm at either the affected remote unit or the affected master unit can also result in generation of an alarm at the other of the two units.