Based on the fact that all objects naturally emit a broad spectrum of electromagnetic radiation, Passive Millimeter Wave Imaging, under development by Millitech Corporation, offers the possibility of rapid detection of metallic and nonmetallic weapons, plastic explosives, drugs, and other contraband concealed under multiple layers of clothing from a distance of up to 12 feet. Low-Frequency Electromagnetic Radiation, under development by the Raytheon Company, involves illuminating an individual with a low-intensity electromagnetic pulse and then measuring the time decay of the reradiated energy from the metal objects carried by the person. The intensity and time decay of the secondary radiation can be characterized and the "signatures" identified as a gun or nonthreatening metal object. Magnetic Gradient Measurements, a concealed weapons detection initiative being explored by the Idaho National Engineering Laboratory, uses a proven technology used in mineral exploration, environmental characterization, military navigation, and submarine detection. This technology is based on passive sampling of the earth's magnetic field. Local aberrations in the magnetic field produced by ferromagnetic objects, such as guns and knives, can be detected by extremely sensitive magnetometers. Other joint Federal Government efforts in developing weapons detection technologies are briefly mentioned: Low-level Scattered X-Rays and Computer Image Processing, Millimeter Wave and Long Wave Infrared Receivers, Radar and Ultrasound, and a Low-Frequency Magnetic Imaging System.