Constitutional Validity of Lie Detector Tests

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(Author: Muskan Krishnani, pursuing B.B.A,. LLB (Second Year) from Amity University, Chhattisgarh.)

The Constitution of India was drafted as The Law of The Land to promote the quality of basic existence of the human being and to protect various natural rights available to them. And any law or practice which abrogates or is in contradiction to this law of land is considered as constitutionally invalid.

Lie Detector Tests

These tests are also known as Deception Detection test and generally are considered as “step to aid” the investigation process of a crime. These are scientific tests employed in criminal investigation by the investigating agencies, upon accused or any witness associated with the trial so as to know the truth or facts of the case. Techniques such as Narco-analysis, polygraph and brain-mapping are employed to conduct such tests. Although, these tests lacks accuracy and have probability of high error rates.


It is also known as truth serum test which is a method of injecting drugs such as sodium pentathlon into the body of the subject so as to compel him to enter into the phase of anesthesia. As a result of such experiment, the subject becomes more suggestible and confessional rather than wilful and his response is spontaneous because of deprivation of self control and reasoning capability to manipulate the answers. The person is generally into unconscious state of mind and discloses actual facts involved in the case.

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But the administration of inappropriate dosage of such drugs can cause the subject to enter into state of coma or even can cause death. It involves injecting and administering drugs and even pinching or slapping the subject to answer the questions. Also as the person is in semi-conscious state, his responses are involuntary and may also lack reliability.


As rightly stated, “polygraphy is the technique to check deception of truth by a subject juxtaposed with the veracity of his statement. ”[i]  Under this scientific technique, the examiner ask questions and measures the involuntary psychological changes such as heartbeat rate, blood pressure, perspiration, pulse, skin reflex, etc and then prepares a chart of such measures observed to infer the opinion that whether the subject is telling the truth or a lie. It is used as a method to connect the link between the bodily responses and psychological process.

The reading of the graph reveals the deviation in the multiple psychological parameters and these reactions are examined by the expert to know the truthfulness in the responses answered by the subject. However, such changes in the body of the subject may also be due to fear, nervousness, anxiety, etc. Hence, in this method as well, there is lack of accuracy.


This scientific technique is also known as P-300 and was designed and developed by Dr. Lawrence Farewell to study the mind of the subject. In this test, the subject is interrogated by the examiner to discover the fact that whether a particular imagine or picture is known to the mind of the subject or is he friendly to such picture. Basically, the objective is to find the link between the picture that is related to the crime scene or some particular fact of the case and the mind of the subject. Such revelation discloses the connection of the accused or the witness with the case in the matter.

Some sensors are attached to the mind of the person and the computer and MERMER brain waves are emitted when the crime scene picture or sound is familiar to the mind of the person. This test helps to analyze the relevant knowledge possessed in the mind of the person about the case or any fact.

Constitutional Validity of Lie Detector Tests

All scientific techniques to detect lie are very useful for the investigating agencies in the process of investigation. But these techniques are not very reliable and often lacks level of accuracy. The courts in India had time and again dealt with the issue of constitutionality of such tests.

These tests are in contradiction to Article 20 and 21 of The Constitution of India, 1950.

Article 20 deals with the protection in respect to conviction for certain offences. Article 20(3) entails that “no person shall be compelled to be a witness against himself.” It deals with the right against self-incrimination. The accused has the right to remain silent.

The Apex Court in the case of Selvi v. State of Karnataka [ii], had held that the no person shall be forced to undergo these scientific process in relation to investigation of case or otherwise. If this test is conducted without the consent of the accused, then it would amount as compelling or forcing accused to yield evidence against himself. It is in direct violation to Article 20 of the Constitution as the right aims to ensure reliability as well as voluntariness in the evidence produced by the accused. The court in this case distinguished between physical and testimonial evidence. Hair, blood, semen, fingerprints, etc can be considered as physical evidence but the results of these tests are considered as testimonial acts.

However, the court also stated that if the subject willingly agrees to undergo such examination tests, then the same doesn’t amounts to violation of the fundamental rights and information or material fact revealed during such tests can also be presented before the court as an evidence in accordance to Section 27 of The Indian Evidence Act, 1872.

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The act of compulsion to administer such tests is also against Article 21 i.e. Right to life and personal liberty. Article 21 includes within its ambit the right to privacy as was declared in the case of K.S.Puttaswamy V. Union of India[iii] and right to fair trial as observed in the case of Zahira Habibullah Sheikh and Ors. V. State of Gujarat and Ors. [iv]

The test of narco-analysis interrupts with the activities of the brain to extract information and various mental thoughts and processes can also be extracted which amounts to violation of the privacy of the subject. Such test when done involuntarily, without the consent of the subject, infringes their fundamental right to privacy.

The concept of the fair trial includes the right against self-incrimination to the accused and compelling the accused to provide evidence against himself by undergoing such tests, violates the right to fair trial of the accused.


The different scientific techniques are useful but such techniques shall only be adopted in case the accused or the witness are willing to undergo such tests, otherwise forceful compulsion order by the court to undergo such tests is in violation to the rights guaranteed to the accused. He is presumed innocent until proven guilty by the prosecution and derogation of his right of fair trial is unconstitutional.

Although, the ultimate objective of the state is to promote welfare of the people and provide safe and sound environment to the people by prevention of crime and punishing the culprits but to adopt strategies to deny fair trial to the accused is outrightly unconstitutional. Accused cannot be entitled to inhumane or barbarous treatment.

[i] B.B Nanda and R.K. Tiwari, Forensic Science in India, A Vision for Twenty First Century 213

[ii] AIR 2010 SC 1974

[iii] (2017) 10 SCC 1

[iv] (2006) 3 SCC 374.