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The accurate and timely discovery of radio receivers can assist in the detection of radio-controlled explosives. Superheterodyne receivers emit low-power radio signals during normal operation. These are known as unintended emissions. In this paper, the unintended emissions of superheterodyne receivers are analyzed. Such receivers are exposed to known stimulation signals, and their behavior is measured. Recorded emissions demonstrate that it is possible to inject arbitrary signals into a radio's unintended emissions using a relatively weak stimulation signal. This effect is called stimulated emissions. A novel detection system that uses these stimulated emissions is proposed. The performance of this system is compared with passive-detection techniques using artificially generated emissions signals. The proposed system offers a 5- to 10-dB sensitivity improvement over existing techniques.