The systems are designed to detect and analyze incoming electronic signals received from the sensor cable, and then to generate alarms from signals which exceed pre-set conditions. The systems have adjustable electronics to permit installers to change the sensitivity of the alarm detectors to the suit specific environmental conditions. The tuning of the system is usually accomplished during commissioning of the detection devices. Advantages: Relatively inexpensive compared to other systems and easy to install. Disadvantage: Older systems may have a high rate of false alarms caused by wind and other distances, although newer systems use DSP (digital signal processing) to process the signal and greatly reduce false alarms in some cases. Taut wire fence systems A taut wire perimeter security system is basically an independent screen of tensioned tripwires usually mounted on a fence or wall. Alternatively, the screen can be made so thick that there is no need for a supporting chain-wire fence. These systems are designed to detect any physical attempt to penetrate the barrier. Taut wire systems can operate with a variety of switches or detectors that sense movement at each end of the tense wires. These switches or detectors can be a simple mechanical contact, static force transducer or an electronic strain gauge. Unwanted alarms caused by birds and other animals can be avoided by adjusting the sensors to ignore objects that exert small amounts of pressure on the wires. This type of system is vulnerable to intruders digging under the fence. A concrete footing directly below the fence is installed to prevent this type of attack. Advantages: low rate of false alarms, very reliable sensors, and high rate of detection. Disadvantages: very expensive and complicated to install. Fiber optic cable A fiber-optic cable can be used to detect intruders by measuring the difference in the amount of light sent through the fiber core. A variety of fiber optic sensing technologies may be used, including Rayleigh scattering or interferometry, If the cable is disturbed, the light will be changed and the intrusion detected. The cable can be attached directly to a chain-wire fence or bonded into a barbed steel tape that is used to protect the tops of walls and fences. This type of barbed tape provides a good physical deterrent as well as giving an immediate alarm if the tape is cut or severely distorted. Advantages: Being cable-based, very similar to the microphonic system and