lie-detector test

In this article, Ritika Agarwal from Institute Of Law Nirma University, Ahmadabad discusses All you need to know about laws on lie detector tests.


  • The lie-detector test is a kind of an activity where the accused, suspect, witness or any other person is supposes to tell truth when asked by examiner.  They are also known as Deception Detection test and have wide moral, scientific, legal significance in the society.
  • These test such as narco analysis, polygraph, brain mapping are helpful to investigators in detecting the lies and finally, increase the efficiency of the investigation. It is ardently claimed by investigation agency that no doubt all the information received from the accused can’t be used by them as evidence in the court but still it is a better way to extract information rather than using “Third-degree methods”.
  • Now the main debate is whether the use of inhuman derogatory techniques justified by our constitution? Whether they are violative of basic fundamental rights of accused or any person who is a subject? This article is basically focusing on settled position of law of lie detectors in India decided by Apex court and its good and bad aspect.

Evidentiary value of lie-detector tests

In order to understand whether these tests are reliable or not for this first we need to have crystal clear understanding of how they are conducted and what impact they have on the subject.

Polygraphy method

The theory initiating this test is that when a subject (person) is lying to the questions asked by the examiner then his body will produce different physiological responses than he produces in normal course which would be detected by examiner by noting measures such as heart rate, blood pressure, respiratory rate, skin conductance and electromyography as few instrument are stick to the subject for recording these measures.

As we know in theory everything looks easy but in practice, it is quite difficult to implement. This same problem is attached with all these Deception Detection Tests. Let’s have a look at what problem could arise while conducting this test. The measured changes in physiological responses

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Let’s have a look at what problem could arise while conducting this test.

  • The measured changes in physiological responses are every time not aroused because of lying and deception but sometimes it could be provoked by anxiety, fear, nervousness, confusion or any other emotions.
  • As well as condition of examination room can also build falsification in reply recorded by the examiner. In spite of this the mental condition of subject plays a most important role.
  • If a person is in depression or not sane or in a state of hyperactivity then it could produce much-distorted results which would ultimately frustrate the core reason of conducting this test.
  • There can be errors because of loss of memory of subject or any other factor which maintains the person’s mental state.
  • But the main failure of this test arises when person deliberately attempts to produce different physiological responses to the question in order to manipulate the examiner so that he can mark the answer as truth rather than a lie.
  • The drawback is examiner can’t make difference between manipulative and genuine responses of the subject. So by looking at all its drawbacks, it can be concluded that they can’t be used as error free pieces of evidence in the court.

Narco Analysis

  • This test is associated with intravenous administration of a drug which forces person to enter into some kind of anesthetic stage. This hypnotic trance stage is helpful for investigators as in this stage the person is more likely to give out concealed information which he never discloses in conscious state.
  • It is useful as it extracts out the hidden conflict in the person’s mind and unsettled feeling regarding past events. The discoveries can aid the investigators to find out the important pieces of evidence or to corroborate pre-existing testimonies and prosecution theories.
  • It is also helpful for accused sometimes if he wants to prove his innocence by this test no doubt the results are not admissible in the court but it supports the case of accused to a greater extent.
  • This test could prove to be useful for activities such as to refresh the memory of witness and to confirm the mental state person to stand trial.

Drawbacks of Narco Test

  • But there are major drawbacks of this test also such as some subjects are capable of preserving their strength to deceive in the anesthetic state also, on the other hand, some can become greatly flexible to questioning.
  • Now, this is specifically troubling because the questions prepared by the investigators may lead to incriminatory responses. Even the drug given didn’t guarantee that the person will only tell the truth.
  • The answers given in a hypnotic stage are not given voluntarily or in an understandable state of mind. Therefore, they can’t be used as evidence in the courts.
  • This test when carried out without consent raises several core issues such as physical incursion on the body by inserting syringes and various agonizing stimuli like pinching, shaking, slapping and such kind of activities to wake a person from half sleep to answer the questions.
  • On the other hand, it also causes mental assault by having unregulated access to sheer private information of the person. However, this test accepted in Second World War but it has not been backed by satisfactory research to legitimize its claims.

Brain Mapping techniques

  • It is also known as “P 300 waves test”. It is a method of discovering whether a person is friendly with some information by gauging the activity in the brain that is prompted by disclosure to selected stimuli.
  • This test consists of examining and measuring ‘event-related potentials’ (ERP) i.e. electrical waveforms emitted by the brain after it has absorbed an external event[1].
  • This whole test is based on the theory that whenever the person is exposed to some pictures, videos, words which contain some relevant (which are related to crime scene or in any manner to a case) and some irrelevant stimuli so that the examiner can record the functioning in his brain when the person is exposed to these stimuli to which he is familiar with.
  • The test has to be performed in an air conditioned and insulated room so to avoid discrepancies rising out of weather conditions.

Drawbacks of brain-mapping techniques

  • The main drawbacks of this test is that it wholly depends upon the familiarity of the subject to the crime scene or any related information but this can be present in person’s mind because of the exposure to the pictures and videos through media or by looking at or reading such things in newspapers, magazines etc or maybe he was just a mere bystander when crime took place.
  • So it can’t be inferred from the test that if the person have some knowledge about such stimuli then he must be related to the crime.

Of these tests, which one has an evidentiary value. Which test is accepted by the Courts in India?

The Apex court overruled various high court judgments and decided that use of narco analysis, polygraph, and brain mapping tests violated subject’s right against self-incrimination in contravention to Article 20(3) of Indian constitution[2]. The article states that “No person accused of an offence shall be compelled to be a witness against himself[3].

According to the various judgments given by high courts regarding this matter, it can be inferred that only if a statement made is incriminating in nature and then used as evidence in court could lead to a violation. Even the Delhi court said that the statement discovered out of these tests can be used as corroborative evidence[4].

The Supreme Court dropped all these judgments and decided that compelling a person to go through these deception detection tests will automatically amount to the requisite compulsion, despite the absence of physical harm done to the administering during the test[5].

Secondly, the court said that because the responses given during these tests are not given consciously or voluntarily thereafter individual have no right to decide whether to answer or not so the responses arises out of all three test amount to the requisite compelled testimony to violate Article 20 (3)[6]

Finally, Supreme court finally dismissed all the arguments and take into considerations the constitutional rights of the accused such as right against self-incrimination, substantive due process rights and the court gave the core understanding of these rights and held used of these three tests violative of constitutional rights.


With all due respect to the decisions given by the Hon’ble Supreme Court on the legality or illegality of lie-detector tests some questions still remain unanswered. The court left open the probability of wrong use of these test as they gave a narrow exception that if the test is carried out by voluntarily given consent of the subject to that test then it can be used as evidence in court. But the dilemma is that even the person is well informed with the consequence of his consent and thereafter voluntarily gave consent then also the consent can’t be said to be given voluntarily. It is a problematic stance.


[1] Smt Selvi & Ors. V State of Karnataka, (2010) 7 SCC 263

[2] Ibid, pg 165.

[3] Constitution Of India 1950,  Art 20(3)

[4] Sh. Shailendre Sharma v State, Crl. WP No. 532 of 2008, at 37

[5] Supra note 1, at 158, 165.

[6] Ibid, pg 161, 165


  1. NTRO is allegedly using MEMORY/BRAIN WAVE READING equipment which is similar to narcoanalysis equipment on small business owners, private citizens, without a legally valid reason to steal trade secrets. Since wireless technology is used, it is very difficult to prove that the memory robbery. The business owners are facing great losses because of the trade secret theft and their correspondence is also stolen by raw/cbi/security agency employees for 9 years.
    What are the legal options available to the small business owner, whose correspondence and trade secrets are ROBBED to end the robbery, since ntro is not covered under RTI


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