Do-it-yourself alarm for home and summer cottages

Recommendation points

• Basic principles of building a security perimeter
• Methods for identifying violations of the regime
• Varieties of sensors
• Principle of operation and connection of sensors
• Control unit or universal controller
• Alarm logic

When you need to keep your property safe, burglar alarms are the most obvious choice. In this article we will talk about the principle of operation of alarm systems and the basics of building security systems, both on standard solutions and on devices of individual configuration.

Typical solutions for alarm systems can be installed independently without problems, but they are not always able to provide a sufficient level of security. The main reason for this is their typical nature, which means that these schemes can be studied by intruders to bypass protection. Therefore, a truly unprecedented level of reliability is provided only by custom-designed security systems..

Basic principles of building a security perimeter

On the printout of the plan of a room or site, you should mark the protected areas and the main ways of unauthorized entry. In a house, it can be windows and doors, an underground floor, an inner lada of an attic.

Conditionally, the building security perimeter can be divided into three levels:

1. Detection of intrusion through windows, doors, etc. Each opening into which a person can theoretically enter must be taken under control.
2. Detection of the presence of a person inside the protected premises.
3. Tracking especially valuable objects. This includes safes, paintings, display cases, etc..

Protection against penetration into the site implies the installation of a continuous security perimeter along the fence line. Identification of people passing through the gate is done by an access control system, usually RFID tags or cards are used.

Getting the outer perimeter to work is difficult due to the high probability of false positives on animals. Therefore, the detectors are placed in such a way that they react only to a person: they place the first and second contours at different heights, determine the most probable routes of movement, etc..

Methods for identifying violations of the regime

There are two ways to detect a person in a protected area. The first is to control the displacement or destruction of natural barriers: doors, windows, fences, etc..

The second method involves continuous monitoring of the environmental parameters on the territory or in the room that accompany a person’s stay: temperature, changes in the internal volume of the room, vibration, noise, etc..

None of the methods have clear advantages, but their combination provides an additional guarantee of protection. It is also important that all means of observation and detection are located covertly, and it was impossible to identify them with a cursory examination..

Varieties of sensors

Human presence detection is often handled by infrared sensors. They are quite versatile, but have a limited range and do not detect a target behind an obstacle..

Beam sensors are located in pairs, exchange light pulses. If the gap between the sensors is violated, they are triggered. They are good for perimeter security, but sometimes they are easy to get around, a person, for example, can crawl under the beam.

Capacitive and radio wave sensors are distinguished by their high reliability. They monitor the state of the indoor environment, react to changes in the internal volume or the appearance of a foreign body. They have high sensitivity and require correct adjustment.

Opening sensors are based on the operation of a reed switch. They are triggered to move away from the magnet sensor, which happens, for example, when a window is opened.

Certain types of sensors react to glass breakage. Acoustic detectors are triggered by a specific sound, vibration detectors are attached to the glass unit and respond to vibration.

Principle of operation and connection of sensors

Most security sensors have a built-in information processing algorithm. For example, infrared sensors do not transmit data from photo detectors to the central unit. When a heat spot appears, they simply work and open the circuit, which is determined by the control unit as a violation of a certain zone. Such sensors are classified as “dry contact”, they have three connection wires: two power supplies and one for monitoring the open circuit. Possibly an additional wire from the tamper.

Application diagram of various sensors

The sensors are configured by two or more verniers, which determine the sensitivity, range and other parameters. Combined sensors have separate relay outputs, the circuit of which is opened when triggered by various factors. They, like the tamper relay, can be connected separately or in series. In this case, the control unit will not determine the cause of the activation, but will simply register violation of the security zone..

Control unit or universal controller

The assembly of a standard signaling complex circuit is quite simple. The kit contains a detailed assembly diagram and all the conductors necessary for connection. The sensors are connected to the receiving and control unit, which monitors their condition and recognizes the actuation of individual zones. The unit is also connected to a control panel with a pin-pad, a zone status indication module and data transmission devices via the Internet, GSM or radio signal.

Freely programmable logic controllers (PLCs) can be used instead of standard control units. Most often they are used to control complexes without connecting to security panels. The advantage of this method is more flexible configuration of operating modes and the ability to use one device to combine security, fire alarm and home automation.

An example of an alarm connection diagram on the Wiren Board controller

Working with a PLC often requires specific knowledge in programming and circuitry, but there are exceptions. Modern devices are programmed via a web interface, for example, a Wiren Board controller, controlled via Android or iOS applications – “XITAL”, programmed using light SMS commands – CCU. As a rule, they support a wide range of connected and compatible devices, support different types of sensors, which is important for combining several automation systems in one center. In addition, in addition to security functions, they are able to monitor the “weather in the house”, turning on or off heating devices according to a given program.

Alarm logic

The simplest example of how an alarm works is a thin wire stretched under a fence. When it is broken, the power supply circuit of the relay opens, which supplies voltage to the sound and light warning devices.

Almost all alarm systems work on this principle, however, they are able to monitor several dozen sensors simultaneously. If at least one of them is triggered, the system notifies the owner or operator of the private security company about the violation, indicating a specific reason.

This scenario is very primitive, there is always a risk of accidental activation, especially in perimeter security. More flexible work algorithms are set individually by PLC programming.

For example, when an external security perimeter sensor is triggered, the system enters a high alert mode, interrogates the sensors for their operability, and turns on video surveillance. Any subsequent violation of the security zones will trigger an alarm. And if there are no further changes, the system will switch to standby mode after a specified time..

This approach allows you to unify the security system and make it less predictable for intruders..