Sensor types Security alarm

1 sensor types

1.1 hermetically sealed reed switches
1.2 passive infrared detectors
1.3 infrasound detectors
1.4 ultrasonic detectors
1.5 microwave detectors
1.6 compact surveillance radar
1.7 photoelectric beams
1.8 glass-break detection
1.9 smoke, heat, , carbon monoxide detectors
1.10 motion sensors
1.11 driveway alarms
1.12 vibration (shaker) or inertia sensors
1.13 passive magnetic field detection
1.14 e-field
1.15 microwave barriers
1.16 microphonic systems
1.17 taut wire fence systems
1.18 fibre optic cable
1.19 h-field
1.20 security electric fence

sensor types
hermetically sealed reed switches

the hermetically sealed reed switch common type of 2 piece sensor operates electrically conductive reed switch either open or closed when under influence of magnetic field in case of proximity second piece contains magnet. when magnet moved away reed switch, reed switch either closes or opens, again based on whether or not design open or closed. action coupled electric current (typically @ 12v dc) allows alarm control panel detect fault on zone or circuit. these type of sensors common , found either wired directly alarm control panel, or can typically found in wireless door or window contacts sub-components.

passive infrared detectors

a passive infrared sensor used detect motion

the passive infrared (pir) motion detector 1 of common sensors found in household , small business environments. offers affordable , reliable functionality. term passive refers fact detector not generate or radiate own energy; works entirely detecting heat energy given off other objects.

strictly speaking, pir sensors not detect motion; rather, detect abrupt changes in temperature @ given point. intruder walks in front of sensor, temperature @ point rise room temperature body temperature, , again. quick change triggers detection.

pir sensors may designed wall- or ceiling-mounted, , come in various fields of view, narrow-point detectors 360-degree fields. pirs require power supply in addition detection signalling circuit.

infrasound detectors

the infrasound detector works detecting infrasound, or sound waves @ frequencies below 20 hertz. sounds @ frequencies inaudible human ear. due inherent properties, infrasound can travel distances of many hundreds of kilometers. infrasound signals can result volcanic eruptions, earthquakes, gravity waves, opening , closing of doors, forcing windows name few.

the entire infrasound detection system consists of following components: speaker (infrasound sensor) microphone input, order-frequency filter, analog digital (a/d) converter, , mcu, used analyse recorded signal.

each time potential intruder tries enter house, or tests whether closed , locked, uses tools on openings, or/and applies pressure, , therefore or creates low-frequency sound vibrations. such actions detected infrasound detector before intruder breaks in.

the primary purpose of such system stop burglars before enter house, avoid not theft, vandalism. sensitivity can modulated depending on size of house , presence of animals.

ultrasonic detectors

using frequencies between 15 khz , 75 khz, these active detectors transmit ultrasonic sound waves inaudible humans. doppler shift principle underlying method of operation, in change in frequency detected due object motion. caused when object must cause change in ultrasonic frequency receiver relative transmitting frequency.

the ultrasonic detector operates transmitter emitting ultrasonic signal area protected. sound waves reflected solid objects (such surrounding floor, walls , ceiling) , detected receiver. because ultrasonic waves transmitted through air, hard-surfaced objects tend reflect of ultrasonic energy, while soft surfaces tend absorb energy.

when surfaces stationary, frequency of waves detected receiver equal transmitted frequency. however, change in frequency occur result of doppler principle, when person or object moving towards or away detector. such event initiates alarm signal. technology considered obsolete many alarm professionals, , not actively installed.

microwave detectors

this device emits microwaves transmitter , detects reflected microwaves or reduction in beam intensity using receiver. transmitter , receiver combined inside single housing (monostatic) indoor applications, , separate housings (bistatic) outdoor applications. reduce false alarms type of detector combined passive infrared detector, or dual tec brand or similar alarm.

microwave detectors respond doppler shift in frequency of reflected energy, phase shift, or sudden reduction of level of received energy. of these effects may indicate motion of intruder.

compact surveillance radar

compact surveillance radar emits microwaves transmitter , detects reflected microwaves. similar microwave detectors can detect precise location of intruders in areas extending on hundreds of acres. capability of measuring range, angle, velocity, direction , size of target, csr able pinpoint precise gps coordinate of intruder. target information typically displayed on map, user interface or situational awareness software defines geographical alert zones or geofences different types of actions initiated depending on time of day , other factors. csr commonly used protect outside fenceline of critical facilities such electrical substations, power plants, dams, , bridges.

photoelectric beams

photoelectric beam system detect presence of intruder transmitting visible or infrared light beams across area, these beams may obstructed. improve detection surface area, beams employed in stacks of 2 or more. however, if intruder aware of technology s presence, can avoided. technology can effective long-range detection system, if installed in stacks of 3 or more transmitters , receivers staggered create fence-like barrier. systems available both internal , external applications. prevent clandestine attack using secondary light source being used hold detector in sealed condition whilst intruder passes through, systems use , detect modulated light source.

glass-break detection

the glass-break detector may used internal perimeter building protection. glass-break acoustic detectors mounted in close proximity glass panes , listen sound frequencies associated glass breaking.

seismic glass-break detectors, referred shock sensors, different in installed on glass pane. when glass breaks produces specific shock frequencies travel through glass , through window frame , surrounding walls , ceiling. typically, intense frequencies generated between 3 , 5 khz, depending on type of glass , presence of plastic interlayer. seismic glass-break detectors feel these shock frequencies , in turn generate alarm condition.

window foil less sophisticated, outdated detection method involves gluing thin strip of conducting foil on inside of glass , putting low-power electric current through it. breaking glass practically guaranteed tear foil , break circuit.

smoke, heat, , carbon monoxide detectors

most systems may equipped smoke, heat, and/or carbon monoxide detectors. these known 24-hour zones (which on @ times). smoke , heat detectors protect risk of fire using different detection methods. carbon monoxide detectors protect risk of carbon monoxide poisoning. although intruder alarm panel may have these detectors connected, may not meet local fire code requirements of fire alarm system.

traditional smoke detectors technically ionisation smoke detectors create electric current between 2 metal plates, sound alarm when disrupted smoke entering chamber. ionisation smoke alarms can detect small amounts of smoke produced fast-flaming fires, such cooking fires or fueled paper or flammable liquids. newer, , perhaps safer, type photoelectric smoke detector. contains light source in light-sensitive electric sensor, positioned @ 90-degree angles sensor. normally, light light source shoots straight across , misses sensor. when smoke enters chamber, scatters light, hits sensor , triggers alarm. photoelectric smoke detectors typically respond faster fire in early, smoldering stage – before source of fire bursts flames.

motion sensors

motion sensors devices use various forms of technology detect movement. technology typically found in motion sensors trigger alarm includes infrared, ultrasonic, vibration , contact. dual technology sensors combine 2 or more forms of detection in order reduce false alarms each method has advantages , disadvantages. traditionally motion sensors integral part of home security system. these devices typically installed cover large area commonly cover 40 ft 135° field of vision.

driveway alarms

driveway alarm systems can tied security , automation systems. designed alert residents unexpected visitors, intruders, or deliveries arriving @ property. come in magnetic , infrared motion sensing options. driveway alarms can purchased in hard-wired , wireless systems. common in rural security systems commercial applications.

vibration (shaker) or inertia sensors

strain-sensor cable installed on chain-link/barbed-wire fence

these devices mounted on barriers , used detect attack on structure itself. technology relies on unstable mechanical configuration forms part of electrical circuit. when movement or vibration occurs, unstable portion of circuit moves , breaks current flow, produces alarm. technology of devices varies , can sensitive different levels of vibration. medium transmitting vibration must correctly selected specific sensor best suited different types of structures , configurations.

a rather new , unproven type of sensor uses piezo-electric components rather mechanical circuits, can tuned extremely sensitive vibration.

advantages: reliable sensors, low false alarm rate, , midpriced.
disadvantages: must fence-mounted. rather high price deters many customers, effectiveness offsets high price. piezo-electric sensors new technology unproven record opposed mechanical sensor in cases has field record in excess of 20 years.

passive magnetic field detection

this buried security system based on magnetic anomaly detection principle of operation. system uses electromagnetic field generator powered 2 wires running in parallel. both wires run along perimeter , installed 5 /12 cm apart on top of wall or 12 /30 cm below ground. wires connected signal processor analyses change in magnetic field.

this kind of buried security system sensor cable embedded in top of kind of wall provide regular wall detection ability, or can buried in ground. provide low false alarm rate, , have high chance of detecting real burglars. however, cannot installed near high voltage lines, or radar transmitters.

e-field

this proximity system can installed on building perimeters, fences, , walls. has ability installed free standing on dedicated poles. system uses electromagnetic field generator powering 1 wire, sensing wire running parallel it. both wires run along perimeter , installed 800 millimetres apart. sensing wire connected signal processor analyses:

amplitude change (mass of intruder),
rate change (movement of intruder),
preset disturbance time (time intruder in pattern).

these items define characteristics of intruder , when 3 detected simultaneously, alarm signal generated.

the barrier can provide protection ground 4 metres of altitude. configured in zones of 200 metre lengths depending on number of sensor wires installed.

advantage: concealed buried form.
disadvantages: expensive, short zones mean more electronics (and higher cost), , high rate of false alarms cannot distinguish pets humans. in reality not work well, extreme weather may cause false alarms.

microwave barriers

advantages: low cost, easy install, invisible perimeter barrier, , unknown perimeter limits intruder.
disadvantages: extremely sensitive weather; rain, snow, , fog, example, cause sensors stop working, , need sterile perimeter line because trees , bushes or blocks beam cause false alarm or lack of detection.

microphonic systems

microphonic systems vary in design each based on detection of intruder attempting cut or climb on chainwire fence. microphonic detection systems installed sensor cables attached rigid chainwire fences, specialised versions of these systems can installed buried systems underground. depending on version selected, can sensitive different levels of noise or vibration. system based on coaxial or electro-magnetic sensor cable controller having ability differentiate between signals cable or chainwire being cut, intruder climbing fence, or bad weather conditions.

the systems designed detect , analyse incoming electronic signals received sensor cable, , generate alarms signals exceed preset conditions. systems have adjustable electronics permit installers change sensitivity of alarm detectors suit specific environmental conditions. tuning of system accomplished during commissioning of detection devices.

advantages: cheap, simple configuration, , easy install.
disadvantage: systems have high rate of false alarms because of these sensors might sensitive. although systems using dsp (digital signal processing) largely eliminate false alarms on cases.

taut wire fence systems

a taut wire perimeter security system independent screen of tensioned tripwires mounted on fence or wall. alternatively, screen can made thick there no need supporting chainwire fence. these systems designed detect physical attempt penetrate barrier. taut wire systems can operate variety of switches or detectors sense movement @ each end of tense wires. these switches or detectors can simple mechanical contact, static force transducer or electronic strain gauge. unwanted alarms caused birds , other animals can avoided adjusting sensors ignore objects exert small amounts of pressure on wires. type of system vulnerable intruders digging under fence. concrete footing directly below fence installed prevent type of attack.

advantages: low rate of false alarms, reliable sensors, , high rate of detection.
disadvantages: expensive , complicated install.

fibre optic cable

a fibre-optic cable can used detect intruders measuring difference in amount of light sent through fibre core. if cable disturbed, light leak out , receiver unit detect difference in amount of light received. cable can attached directly chainwire fence or bonded barbed steel tape used protect tops of walls , fences. type of barbed tape provides physical deterrent giving immediate alarm if tape cut or severely distorted. other types work on detection of change in polarization caused fiber position change.

advantages: similar microphonic system, simple configuration, , easy install.
disadvantage: high rate of false alarm or no alarms @ systems using light leaks out of optical fiber. polarization changing system more sensitive false alarms depend on alarm processing.

h-field

this system employs electro-magnetic field disturbance principle based on 2 unshielded (or leaky ) coaxial cables buried 10–15 cm deep , located @ 1 metre apart. transmitter emits continuous radio frequency (rf) energy along 1 cable , energy received other cable. when change in field strength weakens due presence of object , reaches pre-set lower threshold, alarm condition generated. system unobtrusive when has been installed correctly, care must taken ensure surrounding soil offers drainage in order reduce nuisance alarms.

advantage: concealed buried form.
disadvantages: can affected rf noise, high rate of false alarms, difficult install.

security electric fence

multi-zone security electric fence used on top of physical barrier

security electric fences consist of wires carry pulses of electric current provide non-lethal shock deter potential intruders. tampering fence results in alarm logged security electric fence energiser, , can trigger siren, strobe, and/or notifications control room or directly owner via email or phone. in practical terms, security electric fences type of sensor array acts (or part of a) physical barrier, psychological deterrent potential intruders, , part of security alarm system.

advantages: less expensive many other methods, less give false alarms many other alternative perimeter security methods, , highest psychological deterrent of methods.
disadvantage: potential unintended shock.




^ nasa langley researchers nab invention of year infrasound detection system . www.nasa.gov. 
^ josé chilo, thomas lindblad (2008). wireless data acquisition system using bluetooth technology infrasonic records . computing. 7 (2): 18–21. 
^ girisha durrel de silva & kasun de zoyza. low cost infrasonic recording system (pdf). http://www.comp.nus.edu.sg.  external link in |website= (help)
^ bill waters. how motion sensors work security system . thehomesecurityadviser.com.