easy to install. Allow to cover large perimeters (few tens of Km). Disadvantage: Typically performs in a manner similar to microphonic-based systems but at a higher cost and complexity due to the use of fiberoptic technology. Ported coaxial cable This system employs an electro-magnetic field disturbance principle based on two unshielded (or 'leaky') coaxial cables buried approximately 30 cm (1 ft.) deep and 1 m (3 ft.) apart. The transmitter emits continuous Radio Frequency (RF) energy along one cable and the energy is received by the other cable. When the change in field strength weakens due to the presence of an object and reaches a pre-set lower threshold, an alarm condition is generated. The system is covert after installation. Care must be taken to ensure the surrounding soil offers good drainage in order to avoid nuisance alarms. Advantage: concealed as a buried form. Disadvantages: can be affected by RF noise, difficult to install. Security electric fence Security electric fences consist of wires that carry pulses of electric current to provide a non-lethal shock to deter potential intruders. Tampering with the fence also results in an alarm that is logged by the security electric fence energiser, and can also trigger a siren, strobe, and/or notifications to a control room or directly to the owner via email or phone. In practical terms, security electric fences are a type of sensor array that acts as a (or part of a) physical barrier, a psychological deterrent to potential intruders, and as part of a security alarm system. Advantages: less expensive than many other methods, less likely to give false alarms than many other alternative perimeter security methods, and highest psychological deterrent of all methods. Disadvantage: potential for unintended shock. Wired, wireless, and hybrid systems The trigger signal from every sensor is transmitted to one or more control units either through wires or wireless means (radio, line carrier, infrared). Wired systems are convenient when sensors (such as PIRs, smoke detectors, etc.) require external power to operate correctly; however, they may be more costly to install. Entry-level wired systems utilize a star network topology, where the panel is at the center logically, and all devices home run their line wires back to the panel. More complex panels use a Bus network topology where the wire basically is a data loop around the perimeter of the facility, and has drops for the sensor devices which must include