Intruder alarm

An important principle is that security must be built in depth - otherwise known as defense in depth. In this context, it may be helpful to think of security as a set of concentric rings, where the target is located at the center. Each ring represents a level of physical protection (perimeter fence, building shell, security case) but the number of rings and security resistance will vary relative to the risk. The spaces between the rings may represent other defensive measures such as closed-circuit television (CCTV), security lighting, intruder alarm systems, etc. 

In many cases, it is necessary to complement physical security by the installation of an intruder alarm system in order to achieve the standard of security commensurate to the risk exposure. The scope of protection to be afforded by the alarm system depends on the security risk, but it may embrace fences, windows, doors, roofs, walls, internal areas, yards and external open areas, and vehicles inside and outside buildings. There is a comprehensive range of detection devices, but the choice of detector is critical to ensure that it provides the desired level of protection and is stable in the particular environment. 

Intruder alarms are designed to give a warning of the presence of an intruder within or attempting to enter the protected area. Alarm systems may act as a deterrent to the casual or opportunist thief but they will do little or nothing to prevent a determined intrusion, and to be effective they must provoke an early response from the appropriate authority (in most cases the police). The warning may be a local audible device, but normally the alarm signal is transmitted by the telephone network to a central station operated by a security company on a 24-hour basis. 

Security and safety Intruder alarm Security systems Fire detection systems, with sensors for - temperature - toxic gases like CO, C02, exhaust gases, smoke, etc. - combustible gases like CH4, C2H6 flame detection, fire detectors, caravans with gas detectors, etc. 

In a common type of intruder alarm the detector is positioned at the focus of an encircling set of parabolic mirrors as shown in Fig. 7.10. A moving object causes a succession of maxima and minima in the radiation from it reaching the detector. 

Fig. 7.10 Faceted mirror in an intruder alarm m indicates the positions of the source giving radiation maxima at the detector.

The pyroelectric response of ferroelectrics may be exploited to detect tem-peratnre changes with extremely high sensitivity. The most common devices are nncooled infrared (IR) detectors, which may be used for spectroscopic analysis as well as imaging apphcations. Pyroelectric thin films based on perovskite-type complex oxides, including Pb(Sc,Ta)03 have been deposited by CSD for intruder alarms, gas sensors, and IR cameras. It is anticipated that these thin-film devices will be substantially less expensive to manufacture than existing bulk polycrystaUine devices, which require labor-intensive manufacturing procedures. 

The need for transportability coupled with operator- and intrinsic safety considerations dictates the use of solid state sources operating at low voltage. Of these, Gunn oscillators are the least susceptible to noise and, if locked to a high stability source, are easy to stabilise and to scan in frequency. At lower frequencies they are both inexpensive and widely available as components of intruder alarm systems, but their cost rises rapidly with increasing frequency, and becomes uncomfortable beyond about 100 GHz. 

The spontaneous polarization of a dielectric depends strongly on T, this is the pyroelectric effect that we use for infrared (IR) detection (e.g., intruder alarms and thermal imaging). 

Pyroelectric ceramics can be used to detect any radiation that produces a change in the temperature of the crystal, but are generally used for IR detection. Because of their extreme sensitivity a rise in temperature of less than one-thousandth of a degree can be detected. This property finds application in devices such as intruder alarms, thermal imaging, and geographic mapping. 

ABSTRACT Paper presents problems connected with reliability analysis of the electronic protection systems, with the special regard to the intruder alarm systems. It is presented division of the intruder alarm systems these systems with regard of their structure, and then the analysis for the system with mixed, three branches reliability structure with eventuality of the simultaneously damage of the parallel branches. Utilization of the analysis of reliability structures makes possible the enlargement of the values of the reliability coefficients of the designed systems by accomplishment of the analyses and simulations which allow to select the optimal system structure with regard to the user requirements as well as the characteristics of the protected object (e.g. location of the protected objects in terrain, distances between buildings, etc.). 

In the following part of my paper will be introduced the intruder alarm system, but these questions can be also applied to the another different electronic systems of safety. 

The intruder alarm system can be divided into three principal groups ... 

Figure 1 presents the mixed alarm system with the distracted character, in which the own (switch boards) entries of supervisory tines are used. As the mixed alarm system can be also treated the system in which the concentrated system are connected by the tine RS-232 or RS-485 (or others, but enabling the data transmission between respective alarm, control in the concentrated version, creating the intruder alarm system in the mixed version). 

Figure 2 Presents the example scheme of the intruder alarm system, with three transmit branches A, B, C.

Figure 1. Intruder alarm system - mixed systems. 

Band I telephone, radio, bell, call and intruder alarm circuits, emergency circuits for fire alarm and emergency lighting. 

An intruder alarm system serves as a deterrent to a potential thief and often reduces home insurance premiums. 

Alarm sounders give an audible warning of a possible criminal act. Bells or sirens enclosed in a waterproof enclosure, such as shown in Fig. 14.56, are suitable. It is usual to connect two sounders on an intruder alarm installation, one inside to make the intruder apprehensive and anxious, hopefully encouraging a rapid departure from the premises, and one outside. The outside sounder should be displayed prominently since the installation of... 

Intruder alarm control panel with remote keypad. 

The control panel, such as that shown in Fig. 14.57, is at the centre of the intruder alarm system. All external sensors and warning devices radiate firom the control panel. The system is switched on or off at the control panel using a switch or coded buttons. To avoid triggering tbe alarm as you enter or leave the premises, there are exit and entry delay times to allow movement between the control panel and the door. 

The supply to the intruder alarm system must be secure and tbis is usually achieved by an a.c. mains supply and battery back-up. Nickel-cadmium rechargeable cells are usually moimted in tbe soimder housing box. 

It is estimated that there is now a 5% chance of being burgled, but the installation of a security system does deter a potential intruder. Every home in Britain will almost certainly contain electrical goods, money or valuables of value to an intruder. Installing an intruder alarm system tells the potential intruder that you intend to make his job difficult, which in most cases encourages him to look for easier pickings. 

The type and extent of the intruder alarm installation, and therefore the cost, will depend upon many factors including the type and position of the building, the contents of the building, the insurance risk involved and the peace of mind offered by an alarm system to the owner or occupier of the building. 

Intruder alarm circuits are Band I circuits and should, therefore, be segregated from mains supply cables which are designated as Band II circuits or insulated to the highest voltage present if run in a common enclosure with Band II cables (lEE Regulation 528.1). 

Intrinsically safe circuit Intruder alarm systems Isolation... 

---