The E-Flex II is designed as a primary sensor for medium-security applications or a secondary sensor for high-security applications. It consists of a main processing unit with a sense module and a sensor cable, which is typically attached to a fence surrounding the perimeter to be protected. The sensor cable is a passive detector cable designed on the principle of the triboelectric effect. The system can be used for fences, concrete walls, sheetrock walls, communication cables, pipes that carry communication cables, and subway stations. The standard system is ideal for use with surfaces such as fences that produce a broad range of signal frequencies. However, for some applications the center frequency should be customized. Diagrams and 3 references. (Author abstract modified)