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Introduction Cell phones and other wireless communications devices provide command and control infrastructure for terrorists and insurgents, especially in urban environments. They can also be used to detonate radio controlled improvised explosive devices. The challenge is to locate the origin of signals-of-interest when only non-line-of sight (NLOS) radio signals can be detected. ARGUS Technology Lockheed Martin Advanced Technology Laboratories and the Intelligence and Information Warfare Directorate (I2WD) of the U.S. Army's Communications and Electronics Research Development and Engineering Center (CERDEC) have developed a simple, lightweight, reliable, organic sensor system that a patrol can use to detect and accurately locate nearby radio frequency (RF) emissions in real time. The non-traditional but accurate Agile RF Geolocation for Urban Surveillance (ARGUS) locates these RF emitters and provides real-time situational awareness to warfighters inurban environments. ARGUS is “non-traditional” because it senses only the strength of the RF signal at varying locations within the environment and combines the readings to pinpoint the source of the signal. ARGUS algorithms exploit the sensor network to mitigate the random effects of fading from reflection/refraction caused by urban structures. The ARGUS system: (1) works indoors and out, in urban and rural environments, (2) excels in NLOS environments where traditional DF techniques do not work well, (3) locates signals from 20 MHz up to 2.4 GHz, (4) operates in configurations from a single unit up to 10 sensors, (5) is lightweight and uses a simple whip antenna, and (6) has demonstrated sufficient capabilities for effective tactical responses. ARGUS technology has developed into a mature TRL-7 preproduction system called Invicta that will be evaluated OCONUS in 2007. Concept of Operation ARGUS will be built on a network of hand-held portable sensor/node devices carried by dismounted soldiers, autonomous standalone sensors positioned at strategic locations, and vehicle- mounted units. An ARGUS node includes a low-cost sensor (the RF receiver), a GPS or equivalent capability to identify the location of the sensor, and a display to show the geolocation results to the warfighter. A set of distributed control algorithms are networked so that RF measurements collected at the various sensor/nodes can be coordinated and shared across the network. The ARGUS system will be able to track a moving RF source, locate multiple sources of RF energy and provide a mapping of targets and sensors in the ARGUS network.