Anyone who has had to create perimeter protection systems, especially fairly long ones, perceives words about wireless systems as a fairy tale.
In the estimate for the system, cable products are often the main item, and certainly the main one if you add installation materials and the cost of work.
Armored cables, resistant to weather and rodents.
Wires are needed for two reasons: to transmit the signal to the central post and to transmit electricity to the sensors (as well as video cameras, floodlights, etc.) on the perimeter.
Some systems allow you to save on wires if individual devices are addressable, and the signal is transmitted over one pair of wires from many sections of the perimeter.
For example, in the RS485 format. This is already quite a lot — to run several pairs of wires from each section to transmit several signals (malfunction, alarm, etc.) is very expensive, because the cable costs proportionally to the amount of copper in it.
Further savings to a two-wire line (power and data on one pair of wires) does not make much sense: it does not matter which cable you choose — 2- or 4-wire — compared to the cost of its installation.
The next step is to try to get rid of the wires altogether. That would be great: walk along the fence, stick sensors into the ground, and that's it.
How realistic is that?
Transmitting a signal is quite simple: wireless radio channel systems for transmitting notifications are well-developed, for any reasonable distance.
To transmit a video signal, you can use WiFi or even WiMax (if possible), and regular analog channels (like analog television) can be used provided that the power is low (and therefore the perimeter radius is small, even with directional antennas).
But when it comes to energy transmission, things are much worse.
On extended perimeters equipped with several signaling systems, video surveillance, and lighting, energy consumption is such that it is necessary to install a transformer substation approximately every 10 km – it is almost impossible to transmit 220 V energy over such a distance.
So do wireless perimeter systems exist?
In advertising – they exist.
What is meant by this concept, how legitimate is it to call them wireless, and, most importantly, why are some other systems used besides wireless?
Firstly, there are many systems called wireless, for which this term means the absence of any one wire, and you might not even guess that such a wire exists.
For example, any perimeter detection devices that do not have a sensitive wire element, such as vibration, capacitive or wired radio frequency (wire-wave) systems, are often called wireless.
In this sense, all radio beam products such as RLD and similar ones, as well as single-position and, of course, infrared, both passive and active, are wireless.
There are also many infrared and radio beam sensors (detectors) that are specifically labeled as wireless because they do not require wires to synchronize the receiver with the transmitter (didn't you know that the old two-position radio beam or infrared sensors often required an additional synchronization wire?).
All of these products require power via wires, and their output signal is also designed for wired connection to the data collection system — a good old dry contact.
However, truly wireless systems do exist, and have for quite some time.
For example, quickly deployable battery-powered perimeter alarm systems with wireless signal transmission.
As the name suggests, when creating such systems, the main reason for abandoning wires was not the high cost of laying them, but the length of such a process.
To protect a stopped convoy of vehicles or a landed aircraft, several tripods are quickly set up, adjusted, configured, and the system is ready for operation in a few minutes.
Such systems are usually made on the basis of conventional radio beam detection devices. Recently, video cameras have been included in such systems, although they consume significantly more, especially in winter (heating is usually required) and at night (backlighting is required).
In general, the systems designed as quickly deployable fully fulfill their purpose, but it is inappropriate to use them at stationary sites: they themselves are significantly more expensive than wired analogs, and the battery life, although reaching several days, is only great for short-term security — after several years of operation, constant battery replacements will tire the service personnel.
The usual wireless passive infrared detectors are also truly wireless.
If they are made in an all-weather version, they can be used for perimeter protection. However, built-in transmitters usually have a short range, and in general the use of passive infrared sensors for perimeter protection is questionable.
The probability of a false alarm in the event of sunlight (even reflected from a puddle or wet leaves) is very high, and the probability of detecting an intruder in winter clothing, on the contrary, is low. Therefore, it is appropriate to use such systems only as auxiliary or as extremely cheap quickly deployable systems.
The above-described quickly deployable systems based on two-position radio beam devices are used mainly by such organizations as the Federal Protective Service — for commercial organizations, their price makes their use unprofitable.
However, you can make a wireless, quickly deployable system yourself, taking any regular perimeter sensors, connecting a battery to them for power and any wireless transmitter to transmit a signal.
Recently, systems advertised specifically for stationary objects, powered by solar panels, have appeared.
Unfortunately, the efficiency of solar panels in central Russia in winter is low.
It is enough for traffic lights (10 watts will be enough for them at night), but not so much for a system that includes video surveillance.
Reasonably sized units will be able to provide video cameras with operation only in periodic mode — turning on the camera and backlight briefly to verify the alarm.
This is not very effective, because it does not allow the use of pre-alarm recording. The video surveillance operator will only have to guess whether the branches are swaying from the wind or because an intruder touched them.
Without a video subsystem, such systems should, of course, be quite functional, but how cost-effective their use is compared to conventional ones should be considered in each specific case.
One watt of round-the-clock electricity supply from a solar power plant costs about a thousand rubles.
If you only need a few watts, it is cheaper than pulling a cable for hundreds of meters.
If you need (as is usually the case) about a watt for each linear meter of the perimeter, the cable line will be cheaper.
Even taking into account free energy during the entire period of operation of the complex.