Physical Security and Safety

106

PhysiCal seCurity and safety

Invisible barrier sensors commonly used in exterior applications

are photo-light sensors, microwaves, ported or “leaky” cables, fiber

optic cables, and seismic sensors. Photo-light sensors were explained

above under “Interior Systems”—the facts are the same for exterior

applications. Seismic sensors use motion sensors to detect ground

vibrations. Sensitivity can be set to distinguish normal vibration pat-

terns, with the system alarming when the pattern is exceeded; for

example, the system may recognize foot traffic but alert when vehicle

traffic approaches. Some sensors use electromagnetic fields that are

interrupted by metal objects and produce an alarm. ese systems are

inexpensive to install and maintain. ey a ...