This document describes a house security system that uses a laser beam directed around the perimeter of the house by mirrors. Light dependent resistors (LDRs) are placed along the path to detect any interruptions in the laser beam, which would trigger an alarm. The system is powered by a 3V power supply and uses additional components like transformers, relays, transistors, and diodes. The document provides detailed descriptions and specifications for each component used in the circuit.
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ABSTRACT
House security system protects the house from the attacks of burglars and trespassing from
strangers. Considering the fact that your home is not only your place of privacy but also a store
for your valuable belongings, it is very important to protect it from trespassers and burglars.
The circuit used a laser torch powered by 3V power-supply for generating a laser beam. A
combination of plain mirrors M1 through M6 is used to direct the laser beam around the house to
form a net. The laser beam is directed to fall on an LDR that forms part of the receiver unit. Any
interruption of the beam by a thief/trespasser will result into energization of the alarm. The 3V
power-supply circuit is a conventional full-wave rectifier-filter circuit. Any alarm unit that
operates on 230V AC can be connected at the output.
By the arrangement, house security system energizes the alarm informing about the bulgur and
helps up to take the required steps.
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INTRODUCTION
Our home is one of the top places that make you feel tranquil, secure, and serene. Our home is
also a possible target for attacks from burglars and trespassing by strangers. Considering the fact
that our home is not only your place of privacy but also a store for our valuable belongings, it is
very important to protect it from trespassers. Luckily, with the level of state-of-the-art
technologies available these days, we have plenty of hi-tech options for protecting our home.
And one home security option that has really stood out from the crowd is none other than the
house security system.
Here is a low-cost, invisible laser circuit to protect our house from thieves or trespassers. A laser
pointer torch, which is easily available in the market, can be used to operate this device.
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COMPONENTS
A laser torch
3v power supply
Plain mirrors
Light dependent resistors (LDR)
Step down transformer (X1 and X2)
6v relays
Transistor
Diodes
Switches
Smoothing capacitor
Alarm
COMPONENT DESCRIPTION
A LASER TORCH
Light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up
to a distance of about 500metres.
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3V POWER SUPPLY
The 3v power supply circuit is a convectional full-wave rectifier-filter circuit.
A full-wave rectifier
is a device that has two or more diodes arranged so that load current flows in the same direction
during each half cycle of the ac supply.
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The transformer supplies the source voltage for two diode
rectifiers, D1 and D2. This power transformer has a center-tapped, high-voltage secondary
winding that is divided into two equal parts (W1 and W2). W1 provides the source voltage for
D1, and W2 provides the source voltage for D2. The connections to the diodes are arranged so
that the diodes conduct on alternate half cycles.
During one alternation of the secondary voltage, the
polarities are as shown in fig. The source for D2 is the voltage induced into the lower half of the
secondary winding of the transformer (W2). At the specific instant of time shown in the figure,
the anode voltage on D2 is negative, and D2 cannot conduct. Throughout the period of time
during which the anode of D2 is negative, the anode of D1 is positive. Since the anode of D1 is
positive, it conducts, causing current to flow through the load resistor in the direction shown by
the arrow.
A full-wave rectifier
uses only one-half of the transformers winding at a time. The transformer secondary rated
current should be 1.2 times the DC current of the power supply. The transformer secondary
voltage should be approximately 0.8 times the DC voltage of the unregulated power supply per
side of the center tap or the transformer should be 1.6 times V DC center tapped.
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PLAIN MIRRORS
A plane mirror is a mirror with a plane reflective surface. For light rays striking a plane mirror,
the angle of reflection equals the angle of incidence. A collimated beam of light does not spread
out after reflection from a plane mirror.
A combination of plain mirrors M1 through M6 is used to direct the laser beam around the
house to form a net. The laser beam is directed to finally fall on an LDR that forms part of the
receiver unit.
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Plain mirror
LIGHT DEPENDENT RESISTORS
LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits.
Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but when
they are illuminated with light resistance drops dramatically.
when the torch is turned on, the
resistance of the LDR falls, allowing current to pass through it.
Two cadmium sulphide (cdS) photoconductive cells with spectral responses
similar to that of the human eye. The cell resistance falls with increasing light intensity.
Applications include smoke detection, automatic lighting control, batch counting and burglar
alarm systems.
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GUIDE TO SOURCE ILLUMINATIONS:
Light source Illumination (Lux)
Moonlight __________________________________ 0.1
60W bulb at 1m ______________________________ 50
1W MES bulb at 0.1m ________________________ 100
Fluorescent lighting __________________________ 500
Bright sunlight ____________________________ 30,000
ABSOLUTE MAXIMUM RATINGS:
Dimensions
Voltage, ac or dc peak ______________________ 100V
Current ___________________________________ 5mA
Power dissipation at 25°C _________________ 50mW*
Operating temperature range _________ -25°C +75°C
*Derate linearly from 50mW at 25°C to 0W at 75°C.
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SPECTRAL RESPONSE:
STEP DOWN TRANSFORMER
A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled conductors—the transformer's coils. A varying current in the first or primary
winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic
field throughthe secondary winding. This varying magnetic field induces a varying electromotive
force (EMF), or "voltage", in the secondary winding. This effect is called mutual induction.
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If a load is connected to the secondary, an electric current will flow in the secondary winding and
electrical energy will be transferred from the primary circuit through the transformer to the load.
In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the
primary voltage (Vp), and is given by the ratio of the number of turns in the secondary (Ns) to the
number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current
(AC)voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by
making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around
a ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size
from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units
weighing hundreds of tons used to interconnect portions of power grids. All operate with the
same basic principles, although the range of designs is wide. While new technologies have
eliminated the need for transformers in some electronic circuits, transformers are still found in
nearly all electronic devices designed for household ("mains") voltage.
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SPECIFICATIONS:
For sending unit:
Primary voltage - 230v ac
Secondary voltage - 3v-03v, 100mA
For receiving unit
Primary voltage-230v ac
Secondary voltage- 6v-0-6v,300mA
6V RELAYS
A relay is an electrically operated switch. Current flowing through the coil of the relay
creates a magnetic field which attracts a lever and changes the switch contacts. The coil current
can be on or off so relays have two switch positions and most have double throw (changeover)
switch contacts as shown in the diagram.
Relays allow one circuit to switch a second circuit which can be completely separate from the
first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains
circuit. There is no electrical connection inside the relay between the two circuits, the link is
magnetic and mechanical.
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The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be
as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot
provide this current and a transistor is usually used to amplify the small IC current to the larger
value required for the relay coil.
Relays are usuallly SPDT or DPDT but they can have many
more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily
available. Most relays are designed for PCB mounting but you can solder wires directly to the
pins providing you take care to avoid melting the plastic case of the relay.
The supplier's catalogue should show you the relay's connections. The coil will be obvious and it
may be connected either way round. Relay coils produce brief high voltage 'spikes' when they
are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you
must connect a protection diode across the relay coil.
The Needfor Transient Suppression:
When an electromechanical relay is de-energized rapidly by a mechanical
switch or semiconductor, the collapsing magnetic field produces a substantial voltage transient in
its effort to disperse the stored energy and oppose the sudden change of current flow. A 12VDC
relay, for example, may generate a voltage of 1,000 to 1,500 volts during turn-off. With the
advent of modern electronic systems, this relatively large voltage transient has created EMI,
semiconductor breakdown, and switch wear problems for the design engineer. It has thus become
common practice to suppress relay coils with other components which limit the peak voltage to a
much smaller level.
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Types of Transient Suppression Utilized with Relays:
The basic techniques for suppression of transient voltages from relay coils are shown in Figure 1.
As observed here, the suppression device may be in parallel with the relay coil or in parallel with
the switch used to control the relay. It is normally preferred to have the suppression parallel to
the coil since it can be located closer to the relay (except in the case of PC board applications
where either may be used).
When the suppression is in parallel with the relay coil a bilateral
transient suppressor diode that is similar in V-I characteristics to two zener diodes connected
cathode to cathode (or anode to anode).
Effects of Coil Suppression on Relay Dynamics and Life:
Even though the use of coil suppression is becoming more significant, relays are
normally designed without taking the dynamic impact of suppressors into account. The optimum
switching life (for normallyopen contacts) is therefore obtained with a totally unsuppressed relay
and statements of rated electrical life are usually based on this premise. The successful
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"breaking" of a DC load requires that the relay contacts move to open with a reasonably high
speed. A typical relay will have an accelerating motion of its armature toward the unenergized
rest position during drop-out. The velocity of the armature at the instant of contact opening will
play a significant role in the relay's ability to avoid "tack welding" by providing adequate force
to break any light welds made during the "make" of a high current resistive load (or one with a
high in-rush current). It is the velocity of the armature that is most affected by coil suppression.
If the suppressor provides a conducting path, thus allowing the stored energy in the relay's
magnetic circuit to decay slowly, the armature motion will be retarded and the armature may
even temporarily reverse direction. The reversing of direction and re-closing of the contacts
(particularly when combined with inductive loads) often leads to random, intermittent "tack
welding" of the contacts such that the relay may free itself if operated again or even jarred
slightly.
Based upon the impact on armature motion and optimizing for normally open contacts,
the best suppression method is to use a silicon transient suppressor diode. This suppressor will
have the least effect on relay dropout dynamics since the relay transient will be allowed to go to
a predetermined voltage level and then permit current to flow with a low impedance. This results
in the stored energy being quickly dissipated by the suppressor. Transient suppressor diodes are
available as bi-directional components and permit the relay to be non polarized when installed
internally. Note that if a uni-directional transient suppressor is used, a rectifier diode must be
placed in series with it to block normal current flow and it has little advantage over the use of a
zener diode. The transient suppressor should be selected such that its pulse energy rating exceeds
any anticipated transient such as coil turn-off or motor "noise" found in the application.
SPECIFICATIONS:
6V,100 ohm, c/o relay
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TRANSISTORS
A transistor is a semiconductor device used to amplify and switch electronic signals. It is
composed of a semiconductor material with at least three terminals for connection to an external
circuit. A voltage or current applied to one pair of the transistor's terminals changes the current
flowing through another pair of terminals. Because the controlled (output) power can be much
more than the controlling (input) power, a transistor can amplify a signal. Today, some
transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of
modern electronic devices, and is ubiquitous in modern electronic systems.
There are two types of
transistors, which have slight differences in how they are used in a circuit. Abipolar
transistor has terminals labeled base, collector, and emitter. A small current at the base terminal
(that is, flowing from the base to the emitter) can control or switch a much larger current
between the collector and emitter terminals.
PNP:
The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor between two
layers of P-doped material. A small current leaving the base is amplified in the collector output.
That is, a PNP transistor is "on" when its base is pulled low relative to the emitter.
The arrows in
the NPN and PNP transistor symbols are on the emitter legs and point in the direction of
the conventional current flow when the device is in forward active mode.
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A mnemonic device for
the remembering the symbol for a PNP transistor is pointing in (proudly), based on the arrows in
the symbol and the letters in the name. That is, the PNP transistor is the BJT transistor that is
"pointing in".
Transistor as a switch:
.
Transistors are commonly used as electronic switches, both for high-power applications such
as switched-mode power supplies and for low-power applications such as logic gates.
In a grounded-emitter
transistor circuit, such as the light-switch circuit shown, as the base voltage rises the base and
collector current rise exponentially, and the collector voltage drops because of the collector load
resistor. The relevant equations:
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VRC = ICE × RC, the voltage across the load (the lamp with resistance RC)
VRC + VCE = VCC, the supply voltage shown as 6V
If VCE could fall to 0 (perfect closed switch) then Ic could go no higher than VCC / RC, even with
higher base voltage and current. The transistor is then said to be saturated. Hence, values of input
voltage can be chosen such that the output is either completely off,] or completely on. The
transistor is acting as a switch, and this type of operation is common in digital circuits where
only "on" and "off" values are relevant.
DIODES
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–
voltage characteristic. A semiconductor diode, the most common type today, is a crystalline
piece of semiconductor material connected to two electrical terminals. A vacuum tube
diode (now rarely used except in some high-power technologies) is a vacuum tube with
two electrodes: a plate and a cathode.
The most common function of a diode is to allow an electric current to pass in one direction
(called the diode's forward direction), while blocking current in the opposite direction
(the reverse direction). Thus, the diode can be thought of as an electronic version of a check
valve. This unidirectional behavior is called rectification, and is used to convert alternating
current to direct current, and to extract modulation from radio signals in radio receivers.
However,
diodes can have more complicated behavior than this simple on–off action. Semiconductor
diodes do not begin conducting electricity until a certain threshold voltage is present in the
forward direction (a state in which the diode is said to be forward biased). The voltage drop
across a forward biased diode varies only a little with the current, and is a function of
temperature; this effect can be used as a temperature sensor or voltage reference.
Semiconductor diodes
have nonlinear electrical characteristics, which can be tailored by varying the construction of
their P–N junction. These are exploited in special purpose diodes that perform many different
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functions. For example, diodes are used to regulate voltage (Zener diodes), to protect circuits
from high voltage surges (Avalanche diodes), to electronically tune radio and TV receivers
(varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT
diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit negative resistance,
which makes them useful in some types of circuits.
A modern semiconductor diode is made of a
crystal of semiconductor like silicon that has impurities added to it to create a region on one side
that contains negative charge carriers(electrons), called n-type semiconductor, and a region on
the other side that contains positive charge carriers (holes), called p-type semiconductor. The
diode's terminals are attached to each of these regions. The boundary within the crystal between
these two regions, called aPN junction, is where the action of the diode takes place. The crystal
conducts a current of electrons in a direction from the N-type side (called the cathode) to the P-
type side (called the anode), but not in the opposite direction. However, conventional current
flows from anode to cathode in the direction of the arrow (opposite to the electron flow, since
electrons have negative charge).
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SWITCHES
Switch is an electrical component that can break an electrical circuit, interrupting
the current or diverting it from one conductor to another.
The most familiar form of switch is a manually operated electromechanical device with one or
more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed'
meaning the contacts are touching and electricity can flow between them, or 'open', meaning the
contacts are separated and the switch is nonconducting. The mechanism actuating the transition
between these two states (open or closed) can be either a "toggle" (flip switch for continuous
"on" or "off") or "momentary" (push-for "on" or push-for "off") type.
SPST
Single
pole,
single
throw
One-
way
Two-
way
A simple on-off switch: The two terminals are
either connected together or disconnected
from each other. An example is a light switch.
RESISTOR
A linear resistor is a linear, passive two-terminal electrical component that implements
electrical resistance as a circuit element. The current through a resistor is in direct proportion to
the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's
terminals to the intensity of current through the circuit is called resistance. This relation is
represented by Ohm's law:
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Resistors are common elements of electrical networks and electronic circuits and are
ubiquitous in most electronic equipment. Practical resistors can be made of various
compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such
as nickel-chrome). Resistors are also implemented within integrated circuits, particularly
analog devices, and can also be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial
resistors are manufactured over a range of more than nine orders of magnitude. When
specifying that resistance in an electronic design, the required precision of the resistance may
require attention to the manufacturing tolerance of the chosen resistor, according to its
specific application. The temperature coefficient of the resistance may also be of concern in
some precision applications. Practical resistors are also specified as having a
maximum power rating which must exceed the anticipated power dissipation of that resistor
in a particular circuit: this is mainly of concern in power electronics applications. Resistors
with higher power ratings are physically larger and may require heat sinks. In a high-voltage
circuit, attention must sometimes be paid to the rated maximum working voltage of the
resistor.
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SMOOTHNING CAPACITOR
A capacitor is a device which stores electrical charge. In the simplest terms it can be thought of
as being similar to a rechargeable battery in that it stores power to be used at a later
time. Charging a capacitor is simply a matter of putting voltage across its legs until current stops
flowing
There are many uses of capacitors in renewable energy generation, however one of the
most important is in smoothing the output of a bridge rectifier after it has converted AC
electricity (typically generated by wind turbine generators etc) into DC (used to charge batteries
and power many low voltage devices).
BRIDGE RECTIFIER:
Alternating current (AC) electricity alternates - i.e. the voltage cycles
from a positive maximum to a negative maximum and back again repeatedly. When this
is rectified by a bridge rectifier all negative voltages are rectified into positive voltage as
shown below:
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If this direct current (DC) voltage is used to light an LED for example, then it would flash on and
off repeatedly. This is usually not considered to be desirable and there are many cases where a
fixed voltage is required. In these cases a smoothing capacitor is used.
The smoothing capacitor circuit shown above requires just one capacitor placed across the
output from the rectifier. As the output voltage increases, the capacitor is charged, and as the
output voltage falls back to zero, the capacitor releases its charge (stored energy). The resulting
voltage across the capacitor looks like this:
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CAPACITOR RATINGS:
Capacitors are rated according to their voltage and storage capacity. The larger the capacity of a
capacitor, the more charge it can store and the longer it will take to discharge. However, a very
large capacitor will take a long time to charge initially and so it will take a while before a
constant voltage is output. If the current drawn from the circuit is large, then the capacitor will
discharge quickly and the amount of ripple will increase.
If the voltage in the circuit is above the rated
voltage of the chosen capacitor, the capacitor will be damaged and may even explode. Therefore
it is essential to choose a capacitor with a voltage in excess of the maximum output voltage from
the bridge rectifiers.
CHOOSING A CAPACITOR:
Typically in renewable energy applications a 1000 micro
Farad (1000uF) capacity smoothing capacitor is chosen. These are available with a range of
voltage ratings including 10V (pictured above), 16V, 25V, 35V, 63V with higher voltage
capacitors costing more than those with lower voltage ratings.
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ALARM
Burglar (or intrusion), alarms are systems designed to detect unauthorized entry into a building
or area. They consist of an array of sensors, a control panel and alerting system, and
interconnections. Sensors detect intruders by many methods such as monitoring door and
window contacts, by passive infrared motion detectors, ultrasound, vibration, electric or
magnetic fields, or microwaves. Sensors may be directly wired to a control panel that provides
sensor power, or may communicate wirelessly.
Some alarm systems serve a single purpose of burglar or
fire protection. Combination systems provide both fire and intrusion protection. Intrusion alarm
systems may also be combined with closed-circuit television surveillance systems to
automatically record the activities of intruders, and may interface to access control systems for
electrically-locked doors. Systems range from small, self-contained noisemakers, to complicated,
multi-zoned systems with color-coded computer monitor outputs.
Burglar alarms (or perimeter security systems, perimeter detection
systems, Perimeter protection, intrusion detection systems and other terms for the same
thing) are used in residential, industrial, and commercial properties for protection against theft or
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property damage. Mobile alarm systems protect vehicles and their contents ("car alarms").
Prisons and military facilities use intrusion detection systems for security and control of access.
PHOTO-ELECTRIC BEAMS:
Photoelectric beam systems detect the presence of an intruder by
transmitting visible or infrared light beams across an area, where these beams may be obstructed.
To improve the detection surface area, the beams are often employed in stacks of two or more.
However, if an intruder is aware of the technology’s presence, it can be avoided. The technology
can be an effective long-range detection system, if installed in stacks of three or more where the
transmitters and receivers are staggered to create a fence-like barrier. Systems are available for
both internal and external applications. To prevent a clandestine attack using a secondary light
source being used to hold the detector in a ‘sealed’ condition whilst an intruder passes through,
most systems use and detect a modulated light source.
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PRINCIPLE OF OPERATION
The block diagram of the unit shown in Fig. 1 depicts the overall
arrangement for providing security to a house. A laser torch powered by 3V power-supply is
used for generating a laser beam. A combination of plain mirrors M1 through M6 is used to
direct the laser beam around the house to form a net. The laser beam is directed to finally fall on
an LDR that forms part of the receiver unit as shown in Fig. 2. Any interruption of the beam by a
thief/trespasser will result into energization of the alarm. The 3V power-supply circuit is a
conventional full-wave rectifier-filter circuit. Any alarm unit that operates on 230V AC can be
connected at the output.
The receiver unit comprises two identical step-down transformers (X1
and X2), two 6V relays (RL1 and RL2), an LDR, a transistor, and a few other passive
components. When switches S1 and S2 are activated, transformer X1, followed by a full-wave
rectifier and smoothing capacitor C1, drives relay RL1 through the laser switch.
The laser beam
should be aimed continuously on LDR. As long as the laser beam falls on LDR, transistor T1
remains forward biased and relay RL1 is thus in energized condition. When a person crosses the
line of laser beam, relay RL1 turns off and transformer X2 gets energized to provide a parallel
path across N/C contact and the pole of relay RL1. In this condition, the laser beam will have no
effect on LDR and the alarm will continue to operate as long as switch S2 is on.
Note: LDR should be kept in a long pipe to protect it from other sources of light, and its total
distance from the source may be kept limited to 500 meters.
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ADVANCED SECURITY SYSTEMS
WIRELESS HOME ALARM SYSTEMS:
Wireless security systems are a better form of security systems that has got improved
technology. Standard Burglar Alarm is wired, whereas these wireless security systems works on
RF (radio frequency) waves, which are designed to sense the movements and would instantly
transmit signals to the control unit to notify the event of unauthorized entry. Once the signal is
received by the control unit, it will notify the home owner in a specific way. The signal
transmissions can occur to a maximum of 100 feet.
NETWORK SECURITY CAMERAS
They are a typical web camera that functions as a surveillance camera. Additionally, the NSC
connects to the computer network of the organization, providing real time feed of what is
happening in its facilities. Right now they are used in retail stores, depots, offices, and traffic and
weather control.
DRIVEWAY ALARMS
Wireless driveway alarms are an excellent addition to any alarm system that you may have at
your home. It alerts you before an intruder enters your home or activates your home security
system. Driveway sensor alarm monitors your driveway and alerts you of any incoming visitors
or intruders. If anyone enters your property or monitored area you will be alerted with a pleasant
chime.
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APPLICATIONS
To alert you when someone is around your home or office
It detects trespassers and alerts you by turning on light or alarms or sirens.
To safe guard against theft and bulgary.
At home or business when guests/ visitors are coming up through your way.
To safeguard your valuable belongings.
ADVANTAGES
LIMITATIONS
CONCLUSIONS
REFERENCES
