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  1. Detection of crime

  2. The role of forensic science

  3. Modus operandi and suspect identification

  4. Gathering evidence

  5. Interrogation and confession

  6. Police technology in USA and other countries Police technology

  7. Mobility .

  8. Communication

  9. Computerization .

  10. Criminal identifiction

  11. Equipment and tactics

    • Vests and holsters

    • Arrest - and - control technologies and techniques

    • Police dogs

    • Firearms and explosives .

    • Handguns

    • Shotguns and rifles .

    • Explosives

    • Surveillance systems .

    • Lie detectors

1. Detection of crime . In most countries, the detection of crime is the responsibility of the police, although specialized law enforcement agencies may be responsible for the detection of specific types of crime (for example, customs departments may be responsible for the detection of smuggling and related crimes). The detection of a crime consists of three distinct steps: discovering that a crime has been committed, identifying a suspect, and collecting enough evidence to convict the suspect before a court of law. Criminologists have shown that a high proportion of crimes are discovered and reported by persons other than the police (such as victims or witnesses), but particular types of crimes may involve the consent of a subject, such as drugs or prostitution. or in which there may be no identifiable victim, such as pornography, often undetected until the police take proactive steps to determine whether these crimes are being committed. This may require controversial methods, such as surveillance, interception of communications, infiltration of gangs, and entrapment (for example, by buying from a suspected drug dealer). Once a crime is known to have occurred, it is essential to identify the suspect.

2. The role of forensic science - Forensic science has come to play an increasingly important part in the investigation of serious crimes . One of the first significant developments was identification by fingerprints . It was discovered in the 19th century that almost any contact between a finger and a fixed surface left a latent mark that could be exposed by a variety of procedures. It was accepted in 1893 by the Troup Committee established by the Home Secretary , that no two individuals had the same fingerprints , and this proposition has never been seriously refuted . Fingerprint evidence was accepted for the first time in an English Court in 1902. The original purpose of recording and collecting fingerprints was to establish and to make readily available the criminal record of particular offenders , but fingerprint is now widely used as a means of identifying the perpetrators of particular offences .

Most major police forces maintain collections of fingerprints taken from known criminals at the time of their conviction, for use in identifying these individuals should they commit later crimes. Fingerprints (which may be incomplete) found at the scene of the crime are matched with fingerprints in the collection. According to the British standard, if the sets of fingerprints share at least 16 characteristics, it is considered virtually certain that they are from the same person. For example, fibers can be analyzed by microscopy or chemical analysis to show that fibers found on the victim or at the crime scene are similar to those on the suspect's clothing. Hair samples, and especially skin cells attached to hair roots, can be chemically and genetically compared to samples of the suspect. Many inorganic materials such as glass, paper, and paint can yield considerable information under a microscope or chemical analysis.Examination of a document may reveal that it is a forgery, based on evidence that the paper on which it is written was produced by technology that was not available at the time it was allegedly dated. .

3. Modus operandi and suspect identification . identification of the suspect. The manner in which the crime was committed can also help identify a suspect because many criminals commit the same crimes over and over again. The manner in which the thief entered the home, the type of property stolen, or the type of fraud the victim of the fraud was subjected to can all indicate to the police who is responsible for the crime. Visual identification is often possible but experience has shown that such identification often goes wrong and often results in a miscarriage of justice. Suspects identified in this way are usually asked to participate in a line-up, In which the witness is asked to choose the suspect from a group of people with similar characteristics.

4. Gathering evidence - The identification of the suspect is not the last step in the process: it is essential that the investigating agency gathers enough legally acceptable evidence to convince the judge or jury that the suspect is guilty before conviction. It is common for the police to be reasonably certain that a particular person is responsible for a crime, but to be unable to establish his guilt by legally admissible evidence. To secure the necessary evidence, the police employ a variety of powers and procedures: as these potentially involve interference with the liberty of the suspect (who at this stage should be treated as an innocent person), they are generally under close control. , either by law or by the courts.

An important process is the search of suspicious persons or premises or vehicles. Under common law tradition, most jurisdictions allow searches only when there is "probable reason to believe or reasonable grounds to suspect" that evidence will be found.In some cases, a person may be stopped and searched on the street, provided the police officer reveals his identity and the reason for the search. Searches of private premises usually require a search warrant issued by a magistrate or judge. The law generally allows a search warrant to be issued only if the issuing authority is satisfied, after hearing evidence on oath, that there is good reason to suspect that the evidence, which the warrant usually specifically defines, is in the premises Will be found. In most countries, the judge or magistrate who issued the warrant must be told about the results of the search. Material seized as a result of a search under the authority of a search. The warrant is usually taken into custody by the police for display at any subsequent trial. In the United States, the law has imposed strict consequences on any abuse of this process; Any evidence found as a result of a search that does not comply with the procedures and standards set by the Supreme Court and other courts interpreting the various amendments to the US Constitution, collectively known as the Bill of Rights , is not accepted in it. trial, even if it clearly establishes the guilt of the person accused, and even if the suppression of evidence may prevent the conviction of a person who is clearly guilty. This rule, known as the exclusionary rule, has sparked controversy in the United States and is not generally adopted in other English-speaking countries.

5. Interrogation and confession . The interrogation of suspected persons is an important aspect of the investigation of offences . Usually the aim of the questioning is to obtain an admission of the offence that will lead eventually to a plea of guilty and avoid the need for a contested trial . All English language countries place restrictions on the scope and methods of interrogation in order to ensure that suspects are not coerced into confessions by unacceptable means . In the United States , any suspect who is being interrogated in custody must be offered the services of a lawyer , at the expense of the State if he cannot afford to pay , and failure to advise the suspect of this right ( known as the Miranda warnings , after the case of Miranda v . Arizona ) , results in the rejection of a confession as evidence .

English law follows the same general principle , that a person suspected or accused of a criminal offence is not at any stage in the process of investigation or trial obliged to answer any question or to give evidence . ( There are a few minor exceptions ; for instance , the owner of a motor vehicles is required by law to disclose the identity of the person who was driving the vehicle on any particular occasion , and drivers of motor vehicles may be required to give samples of breath , blood , or urine in certain circumstances ) .For many years, the law relating to confessions in England included a simple rule that prohibited the admission in evidence at trial of any involuntary statement made by an accused person. This rule was supplemented by more detailed rules governing the questioning of suspicious persons by the police, which were drawn up by judges of the High Court and are known as the Judges Rules.

The operation of the judges' rules was a source of controversy for many years, and they have been replaced by a wider range of provisions under the Police and Criminal Evidence Act, 1984. The Act provides that a confession may be admitted in evidence by an accused person provided the court is satisfied that the confession was not obtained by coercion of the person who made it or obtained as a result of any Was or had done such a thing as to make the confession unreliable. Torture is defined to include torture, inhuman or degrading treatment and the use or threat of violence, but no doubt includes other cases (such as interrogation of excessively long periods).

6. Police technology in U.S.A. and other countries .

Police technology - Police technology refers to the wide range of scientific and technological methods, techniques, and equipment relevant to policing. As science has advanced, so too have the technologies that the police have used to prevent and solve crimes. Police technology was recognized as a distinct academic and scientific discipline in the 1960s, and since then a growing body of professional literature, educational programs, workshops, and international conferences has been devoted to the technical aspects of police work.

Although policing in one form or another has existed since the beginning of human civilization, for the vast majority of this history the duties that now fall to the police were accomplished largely by the military as directed by royalty, magistrates, or other governing bodies. Many examples of an incipient police technology date from ancient and medieval times. For example, the ancient Egyptians used detailed word descriptions of individuals, a concept known in modern times as "portrait parle," and the Babylonians pressed fingerprints into clay to identify the author of cuneiform writings and to protect against forgery. Formalized police departments were established in the 19th century, and since that very time technologies have developed rapidly transforming police work into a more scientific endeavour.

7. Mobility -To be effective , police forces must be in close proximity to the citizens they serve . The first and most basic means of maintaining this close contact was the foot patrol . Officers were deployed by time of day and area . were kept geographically small to allow officers to respond to incidents in a timely manner . In larger rural jurisdictions , officers were deployed on horseback . Both foot and mounted patrols continue to be used throughout the world .Foot patrol is used in congested urban areas , in high - density housing complexes , and at special events mounted patrol is also used for special events and for crowd control .

To be effective , police forces must be in close proximity to the citizens they serve . The first and most basic means of maintaining this close contact was the foot patrol . Officers were deployed by time of day ( watches ) and area ( beats ) . Beats were kept geographically small to allow officers to respond to incidents in a timely manner . In larger rural jurisdictions , officers were deployed on horseback . Both foot and mounted patrols continue to be used throughout the world . Foot patrol is used in congested urban areas , in high - density housing complexes , and at special events mounted patrol is also used for special events and for crowd control .

The development of the automobile dramatically transformed police work . Initially , motor vehicles were used not for patrol but rather for deploying officers to foot - patrol beats .

The range of duties performed by police requires a variety of different vehicles . The modern patrol vehicle is routinely fitted with heavy - duty alternators to power the numerous electronic devices and a heavy - duty cooling system to handle engine heat while idling during hot weather . Each vehicle is equipped with an array of electronic devices , including rides , siren and light controls , a public address system , a cellular telephone a radar unit , and , in many jurisdictions , a mobile digital terminal .

In many rural jurisdictions the typical four - door sedan has been replaced by sport - utility vehicles and four - wheel - drive trucks . In areas , where there are no paved roads ( e.g. , open country , beaches , and forests ) , the police use all - tear - rain vehicles and off - road motorcycles . Snow - mobiles and tracked vehicles are used in areas where large snow accumulations are typical .

Some police vehicles have been adapted from military vehicles . Police in South Africa use the Buffel , a vehicle derived from a military armoured personnel carrier , and the Police Service of Northern Ireland ( formerly the Royal Ulster Constabulary ) uses military vehicles in its patrols . In the United States some police departments have converted armoured scout vehicles to assist in high - risk operations . Vehicles built on large chassis can be used to transport a fully equipped command centre to a crime scene or disaster area .

Police departments that patrol a waterfront employ small to midsize open cockpit motorboats . Customs and border - surveillance agencies have access to some of the most complex and exotic watercraft to combat illicit drug running and border incursions . In areas with large swamps , the police use airboats ( flat bottomed boat hulls with an aircraft engine and propeller for propulsion ) .

Various types of aircraft are used in police patrols . Helicopters , the most commonly used aircraft , are often equipped with a high - intensity spotlight that can provide overhead illumination for units on the ground . Another device used by aircraft , a passive infrared unit sometimes called Forward Looking Infrared heat energy emitted by ( FLIR ) , provides night vision . FLIR units can measure objects and living things , enabling ground units to be directed to a particular location .

The police also employ fixed - wing aircraft for operations such as border patrols and drug surveillance , police - personnel transport over long distances , and highway traffic control . They range in size from single - seat planes to Multi engine jet aircraft .

In the 1990s , there was growing interest in bicycle patrols . Bicycle patrol officers are specially trained and equipped with robust but lightweight urban bicycles . Bicycles are very useful for patrolling urban parks , housing complexes , school campuses , and locations where there are multiple large walkways not immediately accessible from the street .

Traffic law enforcement is often conducted by patrol officers on motorcycles or in automobiles . The officers use radar units , either handheld or vehicle mounted , to measure vehicle speed . The most technologically sophisticated of these instruments emit a focused invisible laser beam that makes if possible to gauge the speed of a specific vehicle within a group of moving vehicles .

8. Communication . The vehicles discussed above would be nothing more than efficient conveyances . If police officers were unable to communicate instantly with each other and the public . During the earliest times , communication was accomplished through oral or written orders in an administrative chain of command . As society progressed and the military was used less for domestic peacekeeping , systems of local control were established . In England , the watch- and - ward system evolved to provide citizens with protection from crime . During times of duress , the men on watch would raise the hue and cry to summon assistance from the citizens of the community or , in the case of a larger community , from others already on watch . These watch standers were equipped with various signaling devices , including bells , ratchets , and rattles . With the passage of the Metropolitan Police Act in England in 1829 , the police were formalized into a full - time paid service that was directed by a central command through face - to - face contact between supervisors and subordinates . As urban areas expanded and the police were deployed to more treats over larger geographic areas , this system of human communication became increasingly inefficient . Face - to - face contact gave way to the use of telegraphs in the mid - 19th century , and in the late 1870s police departments began installing telephone systems . In urban jurisdictions call boxes , or street telephones , were placed on beats to enable patrol officers or citizens to alert the central command of a disturbance . In 1917 the police department of New York City began equipping patrol vehicles with a one - way radio receiver that enabled the central command to send emergency messages to officers ; however , this and other early radio communications systems were fraught with technical problems . In 1928 , following several years of experimentation , the police department of Detroit , Mich . , improved the technology to allow regular contact between headquarters and patrol units ; the system developed in Detroit was subsequently the basis of communications systems developed throughout the United States . Two - way radio receivers were first deployed in 1933 in Bayonne , N.J. , and their use proliferated in the 1940s . Rados in patrol cars were eventually supplemented by portable radio transceivers carried by individual officers to allow uninterrupted radio contact between officers and the despatch centre . Police radio - communications systems benefited from the development of computers , which made possible the quick retrieval of information on stolen property , wanted persons , and other police intelligence . Computers were eventually placed in patrol cars . These Mobile Digital Terminals ( MDTs ) enable officers to check licenses , wanted persons lists , and warrants from the patrol vehicle without making an oral radio transmission . MDTs have been supplemented with a wide variety of digital pagers and cellular phones .

9. Computerization . The police were early adopters of computer database technology . In the United States , the National Crime Information Center ( NCIC ) was established in 1967 ; police records were subsequently computerized and made available to police agencies throughout the country . The NCIC's database evade capture . The database contains fingerprints a registry of sexual offenders , enables local police departments to apprehend offenders who might otherwise and warrants for firearms violations ; the system can even search for phonetically and mug shots , and it can be queried for detailed information on stolen vehicles similar names . Similar databases maintained by U.S. States provide access to police to misdemeanour warrants , driver - citation records , and vehicle Early systems of police dispatch involved a single operator who took calls from the public and dispatched officers via radio . The first emergency telephone system was established in 1937 in London , where callers could dial 999 to attract the attention of an operator . Dispatch was improved in the United States in the late 1960s with the establishment of the 911 emergency telephone system . Similar systems have since been adopted also in other countries throughout the world . ownership information .

Computer - Assisted Dispatch ( CAD ) systems such as the 911 system vary in size and complexity . They are used not only to dispatch police quickly in an emergency but also to gather data on every person who has contact with the police . Information in the CAD database generally includes call volume , time of day , types of calls , response time , and the disposition of every call . An enhanced 911 ( E911 ) system adopted in the United States instantaneously identifies the phone number , physical address , and the name of the person who owns the phone from which the call is made . Data maintained in the E911 system sometimes include a history of calls to the police from the caller's location . When the CAD system is linked to a global positioning system , dispatchers can immediately locate the police car nearest the scene of the emergency . Although records are essential for effective police operations , police departments would be overwhelmed without a mechanism for filtering information and making sense of it . Police have long been able to glean similar cases from records available to them , but , until the advent of computer database , systems , such cases were found through the recollection of an experienced investigator . Computerized records systems can be extremely effective in drawing out relationships between past and present cases and suspects . The computer acts like a seasoned detective with an encyclopaedic memory . Systems such as COMPSTAT ( computerized statistics ) , which plot specific incidents of crime by time , day , and location , are used by a variety of large cities , enabling police departments to piece together information and to deploy personnel efficiently . 161 CHP . 20 - SYN . 11 ]

10. Criminal identifiction . - As early as the 1840s in Brussels , photographs were used by the police to keep track of criminals . Such photographs or mug shots , are an essential tool for police investigators . A variety of different formats have been used including most recently , digital images and there is no single universal system employed throughout the world . Digital mug shots have the advantage of being intently transmittable anywhere in the world via the Internet . The science of anthropometry was developed in the late 19th century by Alphonse Bertillon , chief of criminal identification for the Paris police . The Bertillon system which gained almost immediate acceptance worldwide , used. detailed physical measurements of body parts , especially the head and face , to produce a portrait parole .

The technique of DNA fingerprints , which involves comparing samples of human DNA left at a crime scene with DNA obtained from a suspect , is now considered the most reliable form of evidence by many investigators and scientists . Since its development in the 1980s , DNA fingerprinting has led to the conviction of numerous criminals and to the freeing of many individuals from prison who were wrongly convicted . The Combined DNA Index System ( CODIS ) , used by the FBI in the United States , combines computer technology with forensics , enabling investigators to compare DNA samples against a database of DNA records of convicted offenders and others . in the 1980s, when the Japanese National Police Agency established the first practical system for matching prints electronically. The system, called the automated fingerprint identification system (AFIS), allows police to search rapidly through millions of fingerprint records.

The technique of DNA fingerprints , which involves comparing samples of human DNA left at a crime scene with DNA obtained from a suspect , is now considered the most reliable form of evidence by many investigators and scientists . Since its development in the 1980s , DNA fingerprinting has led to the conviction of numerous criminals and to the freeing of many individuals from prison who were wrongly convicted.

The Combined DNA Index System ( CODIS ) , used by the FBI in the United States , combines computer technology with forensics , enabling investigators to compare DNA samples against a database of DNA records of convicted offenders and others .

In criminal investigations biometrics analysis , or biometrics , can be used to identify suspects by means of various unique biological markers . Biometric devices can map minutiae in a single fingerprint and then compare it with an exemplar on file , conducting a retinal or iris scan of the eye , measure and map an entire handprint , or create a digital map of the face . Beometric facial mapping systems , or " facecams , " when linked to offender databases and closed circuit television ( CCTV ) cameras in public places , can be used to identify offenders and alert police . Such systems were implemented in London and other areas of Britain beginning in the 1990s and in several U.S. cities and airports in the early 21st century . Some advocates of biometrics technology have proposed that biometrics data be embedded into driver's licenses or passports to enable security officials to identify suspects quickly . After the September 11 attacks in the United States in 2001 , proponents of biometrics called for expanding its use significantly, arguing that such measures were necessary to protect the United States and other countries from international terrorism .

Critics of the technology contended that it unduly infringed upon the civil liberties of law abiding citizens ;

11. Equipment and tactics

( i ) Vests and holsters - Officers , whether plainclothes or in uniform , carry a variety of equipment with them on service calls . An essential piece of equipment is the bulletproof vest , which covers the torso of the officer and is worn either over or under the uniform shirt . Many are made with the fibre Kevlar and can protect against most handgun projectiles and many types of knives . More robust vests made of ceramic and fibre combination can withstand rifle fire and are used in bomb - disposal operations .

( ii ) Arrest - and - control technologies and techniques . - Non lethal tactics and instruments . Officers routinely arrest suspects in the course of their duties . Although most suspects surrender without incident , occasionally some will resist being taken into custody . Some unarmed techniques for subduing suspects re drawn from various martial arts , such as judo and aikido , and others are based on knowledge of nerve pressure points . Unarmed control tactics are used in most incidents in which the police use force .

Electronic technologies include the stun gun , which delivers an electric charges that causes muscle spasms , pain , and incapacitation ; and the Taser , which fires two barbed projectiles that deliver an electric charge without requiring the officer to come within arm's reach of the suspect .

Tear gas is traditionally used to disperse large crowds . Early aerosol sprays were problematic and were used only sparingly because they vapourized and could affect officers and others in close proximity to the suspect - particularly inside a squad car . Sprays containing capsicum oleoresin , an irritant derived from pepper plants , proved to be more effective than other aerosols , and they possessed the additional advantage of being non - vaporizing .

The less harmful " pepperball , " which combines a compressed air launcher and a projectile filled with capsicum oleoresin , was developed in the 1990s . Because the projectiles break upon impact , they usually do not cause permanent injury , even when fired at close range . The so - called " beanbag projectile , which can be fired from shotguns and grenade launchers ,

(iii) Police dogs . - Dog were first trained for police work at the turn of the 20th century in Ghent , Belg , and the practice was soon copied elsewhere . Although certain breeds with especially keen senses are used for special purposes , such as detecting caches of illegal drugs and explosive or for tracking fugitives and missing persons , the most widely trained dog for regular patrol work in the German shepherd , or Alsatian . Other breeds that are sometimes used include Boxers , Doberman pinschers , Airedale terriers , Rottweilers , Schnauzers , and Bloodhounds .

(iv) Firearms and explosives . In the most exigent circumstances , police may have to use firearms . Police in Britain are generally unarmed , though , beginning in the late 20th century , a growing number of officers there carried guns . In countries in which the police carry sidearms , a wide variety of handguns and long guns are used .

(v) Handguns . The first practical police firearm , the multishot revolver , was patented in 1835 by Samuel Colt . Although slow to be accepted at first , it grew in popularity after the U.S. Government purchased 1,000 of the sidearms for the Mexican War ( 1846-48 ) and after the Yexas Rangers adopted it as their official weapon . In 1851 , the British gun manufacturer Robert Adams introduced the self - cocking double act on revolver . In the United States the revolver has become with few exceptions , the police sidearm of choice for more than a century . Semi - automatic pistols were developed in Germany in the late 19th century by Peter Paul Mauser , whose Mauser rifle became a standard infantry weapon . In 1911 the 0.45 calibre single action semi - automatic pistol developed by theAmerican weapons designer John Browning was adopted by the U.S. military . Although this Browning design dominated the American semi - automatic pistol market , European manufacturers were producing a variety of weapons , particularly double action pistols . Beginning in the 1970s , police departments in the United States slowly began to replace revolver with semi - automatic pistols .

( vi ) Shotguns and rifles .-- The standard police sidearm is strictly a defensive weapon . For offensive operations such as gunfights , more powerful firearms , such as shotguns and rifles , are necessary . Shotguns are capable of firing at variety of ammunition , including buckshot , slugs , tear gas , batons , and grenades . The pump - action of shotgun , which was widely used in police departments from the early 20th century , began to be replaced by the semi - automatic shotgun in the late 20th and early 21st centuries . The lever - action rifle accompanied the lawmen of the American West as they policed their jurisdictions in the 19th century . During the 20th century police continued to use rifles of various descriptions and calibers . From the 1920s until World War II , some police departments in the United States adopted the Thompson sub - machine gun , or tommy gun , a weapon that was also embraced by the criminal underworld . The advent in the late 1960s of Special Weapons And Tactics ( SWAT ) teams brought into service police countersniper units . Weapons used by such teams varied but typically included bolt action light calibre rifles fitted with felescopic sights .

( vii ) Explosives . - Explosives are used only sparingly by police , generally for breaching barricades and as distraction devices . Explosive " flash - bangs , " which generate a loud explosion and a brilliant flash that disorient suspects , are usually tossed by hand or launched from firearms . One variation of the flash bang , used particularly for riot suppression , discharges multiple small rubber balls or baton projectiles .

( viii ) Surveillance systems . - Audio surveillance , or electronic eavesdropping , became practical for obtaining evidence and investigative leads after the development of magnetic recording in the early 20th century . Among the earliest automated surveillance systems were telephone pin registers , which recorded the phone numbers called from a certain surveillance location . Modern systems allow investigators to record the numbers of both incoming and outgoing calls , as well as any conversations . Other technologies enable audio surveillance through covert miniature microphones and radio transmitters and al variety of radio receiving and voice recording equipment . Self - contained wireless microphones are now so small that they can be secreted into virtually any object . Police conduct visual surveillance with binoculars , telescopes , cameras with telephoto lenses , CCTV , and videotape recorders . Cameras fitted with telescopic and other specially lenses have become standard covert surveillance tool . Night vision devices , or " starlight scopes " , can be combined with telescopic lenses , both film and digital cameras , and videotape recorders . Similar to the FLIR units on aircraft , hand held passive thermal - imaging devices allow for convert observation in complete darkness .

The technology has been widely adopted in Britain to monitor public areas . Cameras may be equipped with telephoto or variable power lenses and motor drives . Low light cameras can record images in almost complete darkness : those equipped with infrared emitters can record images in total darkness .The videotapes may be used as evidence in Court to confirm or refute allegations of improper or illegal conduct by police officers .

( ix ) Lie detectors . Throughout history , those responsible for enforcing the law have attempted to develop lie detectors . One interrogation method used in Asia was based on the principle that salivation decreases during nervous tension . The mouths of several suspects were filled with dry rice , and the suspect exhibiting the greatest difficulty in spitting out the rice was judged guilty .

Another precursor of the modern lie detector was employed in India , where suspects were sent into a dark room where a sacred ass was stabled and were directed to pull the animal's tail . They were warned that if the ass brayed it was a sign of guilt . The ass's tail had been dusted with black powder ; those with a clear conscience pulled the tail , whereas the guilty person did not , and an examination of the hands of the suspects revealed the person with the guilty conscience .Scientific advances led to the development of polygraphs in the 1920s .The polygraph is base don the premise that an individual who is lying will have subtle but measurable changes in specific physical indicators . Lie detectors utilize sensors placed on the test subject that record respiration , heart rate , blood pressure , and galvanic skin response or moisture in the fingertips . Taken together under highly controlled interview conditions and interpreted by a trained expert , these measurements may indicate an attempt to deceive . Although the polygraph has proved an invaluable aid to police , its scientific validity has been questioned by some psychologists . Accordingly , the results of polygraph tests are not always admissible in judicial proceedings . Voice stress analyzers , which became commercially available in the 1970s , rely on the detection of minute variations in the voice of the subject . Advocates of voice - stress analysis contend that a lying subject will produce vocal microtremors that can be captured and graphed . Despite its initial promise , the voice stress analyzer has not gained universal acceptance . Other techniques developed in the date 20th century relied on measurements of brain - wave activity and on thermal images of facial skin temperature .



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