When designing a security system based on sensors with high reliability it is important not to counteract that performance with false alarms caused by quality problems in any stage of the system. A fiber-optic continuity sensor may offer the ultimate level of reliability and freedom from false alarms. The bonding of an optical fiber within a barbed steel tape is one way of designing a security system where the electronics and data communication facilities are combined in a modular form. An optical fiber woven security net, composed of cables of various combinations woven into sensor barriers, sets off an alarm when there is a break but operates reliably and continuously. This technology has been developed to meet the requirements of underwater physical security. An output speckle pattern interferogram, which monitors fiber optic cables, is a measure of the fibers' physical displacement. Attenuation sensors, which detect changes in optical characteristics due to temperature variations, have been used to detect attempts to tamper with data communications in local area networks. 7 figures. (Author abstract modified)