What is a perimeter security system?
Today, we can identify the main physical principles used to detect sensors along the perimeter of an object: radio wave, electro-optical, capacitive, inductive, magneto, and vibration sensors.
Please note that the most common types of perimeter sensors use different principles of physical measurement.
1. The operating principle of a radio wave sensor is based on a change in the electromagnetic field strength when a criminal enters the sensor's detection zone. Sensors of this type are usually placed in the ground along the perimeter of a fence, on the walls and roofs of buildings. For its placement, a direct line of sight from the receiver to the transmitter, the absence of vegetation (the technical specifications usually indicate the grass level in centimeters), terrain curvature is not allowed, but due to low sensitivity in the immediate vicinity of the receiver and transmitter, they must cover the area around the detection sites.
Sources of interference may occur near power lines, highways, railways, in the presence of small moving objects (tree branches and bushes, cats, dogs, birds). It should also be noted that it is difficult to adjust many sensors of this type.
2. The operating principle of electro-optical sensors is based on determining the change in the intensity of infrared radiation at the receiving point when an intruder enters the detection zone. As radio wave sensors, infrared radiation propagation, absorption, reflection, refraction, diffraction, and interference phenomena are observed. Some of them are taken into account when creating a sensor and the possibility of implementing the detection process. Depending on the method of forming a material field (infrared electromagnetic wave), sensors are divided into active and passive. Active sensors independently form infrared radiation and control its intensity, and passive sensors use infrared radiation, which is naturally inherent in any object with a temperature above "absolute zero". In turn, sensors can have either one active position, that is, the transmitter and receiver are combined in one housing, or two positions. Optoelectronic sensors are used both indoors and when organizing perimeter boundaries. Sensors should be installed on durable elements, capital surfaces (structures) that exclude vibration. Sensors are installed in such a way as to exclude the possibility of direct or reflected (for example, water surface) sunlight, car headlights hitting the receiving part in order to avoid false alarms. The probability of detecting a criminal can be significantly reduced in the case of optical atmospheric phenomena due to reduced visibility: fog, snow, rain. False alarms can be created by large animals and small insects in the immediate vicinity of the sensor. Despite all the obvious disadvantages, optical-electronic detection devices are widely used in cases where it is necessary to protect the perimeter of small areas where it is difficult to use other types of sensors, for example, when crossing the perimeter of a pipeline. Relatively low cost and ease of installation make them very attractive. Please note that to reduce the probability of false alarms, today many types of sensors use multi-channel ones, allowing to implement different ways of their operation, for example, the logic "AND", "OR". More expensive models use microprocessor processing, which gives additional time for analyzing the alarm pulse.

3. Vibration sensors represent a fairly wide range of equipment based on different principles of operation. Among them are triboelectric, piezoelectric and vibration magnetometers, thin-contact electrically charged and barometric.