Remote controlled transmitters and devices which are switched off, cannot be found by any counter surveillance equipment based on radio scanners. The solution is a debugging device independent from any emission of radio frequencies. Even before using a new room for conferences or after installations, respectively maintenance operations in the room, a basic sweep is absolutely necessary to avoid monitoring by planted devices. The PKI 4200 Non-Linear Junction Detector does not only detect active bug devices but also those which have been switched off. The extremely lightweight unit (only 1.8kg) is a Third Harmonic Junction Detector and important facility for discriminating between false and real targets. The coloured LED display simply shows left GREEN for false and right RED for target. In addition to the customary Geiger audio indicator, the unit also features AM and FM demodulation modes. Direct listening via headphones is possible.