Polygraph or Lie Detector Test


A lie detector test is a psycho-biological examination that uses computerized technology known as a Lie Detector or Polygraph to verify the authenticity of participants’ statements.

Dr. John Larson of the United States developed this procedure in 1921. It is predicated on the concept that when a person lies, there are changes in the body that may be adequately recorded.

The polygraph specialist creates questionnaires based on documentation given by the IO and discussions with individual. The lie detector equipment captures changes in the autonomic nervous system in the subject’s body throughout testing, which serve as the foundation for detecting deception in the report.

The lie detector measures the following autonomic nervous system activities in the form of graphs:

  • Abdominal respiration
  • Thoracic respiration
  • Galvanic skin resistance (GSR)
  • Blood pressure/pulse rate
  • Muscular pressure
  • Finger pulse
  • Skin temperature


The individual is made to lay on a bed and several sensors are attached to his body throughout this operation. Changes in respiration, blood pressure, pulse, respiratory rate, and sweating are all measured by these sensors. During this process, the person is asked certain right standard questions (also known as control questions), and his replies are recorded on a polygraph. Then legitimate questions are asked, mixed in with fillers, and the person’s responses are logged. It has been discovered that when a person lies, his blood pressure and pulse rate rise, as does his sweat. The individual’s reaction to some fillers is also recorded. Because all of these replies are recorded on a polygraph, it is also known as a ‘polygraph test.’ The examination usually lasts around 2 hours.

This test is particularly significant in instances of non-habituated criminals, but it fails in cases of very determined and highly driven criminals since they may readily talk falsehood. The court is not required to grant approval for this inquiry. The results of this test are not admissible in court, although they can give information to investigators.

Guidelines of National Human Rights Commission for Polygraph Test

The National Human Rights Commission issued instructions on the administration of polygraph tests to accused persons in letter number- 117/8/97-8 dated 11/01/2000. The investigating officers are instructed to strictly adhere to the instructions. Following careful study of this critical topic, the Commission has established the following rules for the administration of Lie Detector Tests:

(i) No Lie Detector Test should be administered except on the basis of consent of accused. An option should be given to the accused whether he wishes to avail such test.

(ii) If the accused volunteers for a Lie Detector Test, he should be given access to a lawyer and the physical, emotional and legal implications of such a test should be explained to him by the police and his lawyer.

(iii) The consent should be recorded before a Judicial Magistrate.

(iv) During the hearing before the Magistrate, the person alleged to have agreed should be duly represented by a lawyer.

(v) At the hearing, the person in question should also be told in clear terms that the statement that is made shall not be a ‘confessional’ statement to the Magistrate but will have the status of a statement made to the police.

(vi) The Magistrate shall consider all factors relating to the detention including the length of detention and the nature of interrogation.

(vii) The actual recording of a Lie Detector Test shall be done in an independent agency (such as a hospital) and conducted in the presence of a lawyer.

(viii) A full medical and factual narration of manner of the information received must be taken on record.

General Requirements:

(i) The investigating officer is advised to send a requisition addressed to the Director, State FSL, requesting for a date of polygraph examination. The requisition has to be forwarded either by Superintendent of Police or Sub Divisional Police Officer. While sending requisition, the investigating officer should attach photocopies of all relevant documents such as FIR, statements of subject(s) recorded under Section 161 CrPC, PM Report, Spot visit report, sketch of the spot, a brief case history and photographs, if any. This will enable the experts to understand the nature of the crime, role of the subject(s), and most importantly how, when and where the crime was committed, who were the other accomplices and the motive behind the crime and other selected issues such as disposal of dead body, weapon of offence, vehicle used if any etc.

(ii) The investigating officer is advised to requisition the services of a Polygraph Division only after making a thorough investigation and after collecting relevant documents including physical evidence, mobile call details, PM report, inquest report, injury report, age certificates, etc. In the absence of such details referred to above, it is extremely difficult for the examiner to formulate proper questions and unreveal inconsistencies in the statements of the subject.

(iii) The laboratory will communicate date for consultation with the investigating officer. The expert after going through the facts of the case will prepare questionnaire and communicate date(s) for the polygraph test.

(iv) The investigating officer is required to meet the concerned expert at State FSL, personally for discussion and subsequent examination. Under no circumstances, any officer other than the IO will be entertained.

(v) Before sending requisition, the concerned IO should attach a declaration that he has obtained consent of the subject(s) to undergo the Test as per Article 20(3) of the Indian Constitution and orders passed by the Honorable Supreme Court of India referred to above. Often, it has been observed that the subjects are not informed by the investigating officer, as a result of which the expert has to face problems to obtain consent from the subjects at the time of examination. Invariably this has resulted in inconvenience and wastage of time both of the expert and the IO.

(vi) Only nominated subjects will be examined on date and time fixed by the expert. Fresh dates are to be obtained if additional persons related to the crime are required to be examined.

(vii) As a Polygraph Test is a psycho-physiological test, long journey should be avoided on the date of examination and the subjects may be given sufficient rest and food prior to polygraph examination to ensure qualitative results.

(viii) In case of lady subjects, a lady home guard/constable is required to accompany the subject who will remain present during examination also.

(ix) All minor subjects should be accompanied by their parents/guardians compulsorily who will also countersign the consent form.

(x) In case further session is required, the IO should make his/her arrangements to stay. The IO will also make necessary arrangements for security of the subjects.

(xi) While asking the questions on the equipment, each question is asked after a gap of 25 seconds. This gap is allowed in order to activate and normalize the sympathetic and para sympathetic components of the autonomic nervous system. Marking should be made on the chart at the time of starting of question and end of the question and also indicate the response of the subject on chart (Required in manual polygraph equipment).

Drawback of Lie Detector Test

Let’s have a look at what issues can happen while running this test. The alterations in physiological responses that have been measured:

  • The recorded changes in physiological reactions can also be triggered by worry, fear, uneasiness, bewilderment, or any other emotion.
  • Furthermore, the state of the examination room might lead to deception of the examiner’s response. Regardless, the subject’s mental state is extremely significant.
  • If a person is depressed, insane, or hyperactive, the findings may be greatly affected, which would eventually hinder the purpose of doing this test.
  • There may be inaccuracies due to a loss of subject memory or any other element that maintains the person’s mental state.
  • A person purposefully seeks to induce varied physiological reactions to the question in order to mislead the examiner into marking the answer as true rather than false.
  • The disadvantage is that the examiner cannot distinguish between manipulative and real replies from the individual. Looking at all of the disadvantages, it is clear that they cannot be utilised as error-free pieces of evidence in court.
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