to constantly verify that the positioning of the sensor, based on MEMS accelerometer, remains unaltered from the installation one. MEMS accelerometers’ significant advantages are also given by their small size and high measurement frequency; additionally, they can be integrated with multiple sensors with different functions. Ferrous metal detectors Change in the local magnetic field due to the presence of ferrous metals induces a current in the buried sensors (buried cables or discrete sensors) which are analyzed by the system. If the change exceeds a predetermined threshold, an alarm is generated. This type of sensor can be used to detect intruders carrying substantial amounts of metal, such as a firearm, making it ideally suited for anti-poaching applications. Electrostatic field Sometimes referred to as E-field, this volumetric sensor uses Electric field proximity sensing and can be installed on buildings, perimeters, fences, and walls. It also has the ability to be installed free-standing on dedicated poles. The system uses an electromagnetic field generator powering one wire, with another sensing wire running parallel to it. The sensing wire is connected to a signal processor that analyses: amplitude change (mass of intruder), rate change (movement of intruder), preset disturbance time (time the intruder is in the pattern). These items define the characteristics of an intruder and when all three are detected simultaneously, an alarm signal is generated. The barrier can provide vertical protection from the ground to the height of the mounting posts (typically 4–6 meters of height), depending on the number of sensor wires installed. It is usually configured in zones of about 200 metre lengths. Advantage: High-security (difficult to defeat), high vertical detection field. Disadvantages: Expensive, short zones which mean more electronics (and thus a higher cost). Microphonic systems Microphonic systems vary in design (for example, time-domain reflectrometer or piezo-electric) but each is generally based on the detection of an intruder attempting to cut or climb over a fence. Usually the microphonic detection systems are installed as sensor cables attached to rigid chain-wire fences, however some specialized versions of these systems can also be installed as buried systems underground. Depending on the version selected, it can be sensitive to different frequencies or levels of noise or vibration. The system is based on coaxial or electro-magnetic sensor cable with the controller having the ability to differentiate between signals from the cable or chain-wire being cut, an intruder climbing the fence, or bad weather conditions.