Can You Say No to a Lie Detector Test in Singapore? And Other FAQs

Last updated on May 23, 2018

Featured image for the "Can You Say No to a Lie Detector Test in Singapore? And Other FAQs" article. It features a man taking a polygraph test.

A lie detector or polygraph is a machine that attempts to identify when a person is lying. They are commonly used by law enforcement authorities investigating crimes all over the world, including in Singapore. If you are asked to take a polygraph test, here’s what you should know.

How Does a Polygraph Test Work?

The polygraph attempts to detect lies by reference to certain physiological responses, believed to be indicative of lying, such as irregularities in breathing patterns, blood pressure, pulse and skin conductivity. These are measured by hooking the subject up to the machine via various attachments to the chest and one hand and arm.

The polygrapher then asks a series of questions, some of which are relevant to the crime and some of which are merely intended to set a baseline for a true and false result. The subject is asked to lie to an irrelevant question for the latter.

However, there are no specific physiological reactions that can be consistently associated with lying. Different people’s bodies react differently when they lie. Some people’s breathing pattern changes right before they lie, other sweat a little more, some people’s heart rate increases – but others’ do not.

For this reason polygraph tests are known to be wildly unreliable. Innocent but nervous subjects sometimes fail them and guilty but calm subjects sometimes pass them.

How Can a Polygraph Test be Used against Me?

The short answer is, it can’t, at least not as evidence against you in a criminal case.

In Singapore, and indeed in much of the rest of the world, polygraph tests are inadmissible as evidence against an accused person in a criminal case. This is because its inherent unreliability means that evidence of this kind is more likely to simply create confusion and controversy as to its evidential value rather than actually weigh clearly towards guilt or innocence.

Why Do the Police Use Polygraph Tests?

Even though polygraph tests are inadmissible as evidence in a criminal case, law enforcement agencies still find them useful for deciding whether to recommend prosecution, in cases where they might feel they don’t presently have enough evidence to do so.

Where the police are on the fence about a suspect’s guilt, a failed polygraph test might be enough to make them lean towards recommending prosecution, or at least recommending further investigation, if they feel they have insufficient evidence to secure a conviction.

Conversely, a passed polygraph test might be enough to convince police, in a case where there is little evidence of a person’s guilt, to recommend avoiding wasting further resources on continuing the investigation.

I’ve Been Asked to Take a Polygraph Test. Should I?

If you are asked to submit to a polygraph test, the good news is that the police clearly haven’t decided to recommend prosecution yet. Whether you should take the test is a big question and one that should be considered in light of all the facts of your case. Therefore, if you find yourself in such a situation, you should say you need time to take legal advice before deciding and then immediately call a criminal lawyer.

This is because your response to the police’s invitation will inevitably affect their assessment of your guilt. For example, if you decide to take the polygraph test:

  • And you pass the test, the police may well conclude that you are innocent and take no further action.
  • But if you fail the test, the police may well conclude that you are guilty and recommend prosecution.

On the other hand, if you decline to take the polygraph test, the police may conclude it is because you are guilty and recommend prosecution. They may also want to record another statement from you about the reasons why you chose to decline taking the polygraph test.

If this happens, you should simply state for the record that your decision to decline the test was based solely on legal advice you received. Because your legal advice is covered by solicitor-client privilege, it is difficult to pry any further than that.

If additional possible reasons for refusing the test are suggested to you, such as you being afraid the test will indicate your guilt, you should simply repeat the sole reason already given (i.e. that your decision to decline was based solely on legal advice you received) and ensure that this is the only reason included in any written statement you sign.

Ultimately, internal police decision-making (on matters such as whether to recommend prosecution) is an opaque and secretive process. It is difficult to identify whether certain decision-making criteria are being applied consistently, or if so, what they are.

That’s why it’s important to seek legal advice from an independent criminal lawyer on this important decision rather than simply trust any verbal assurances from police officers about the likely outcome of your decision.

Can I Volunteer to Take a Polygraph Test?

You certainly can but if you do, you probably won’t be given one unless the police believe it would be helpful to them.

Volunteering to take one would certainly tend to suggest innocence though, so if you volunteered to take it while you were being interviewed to prepare your statement, you should ensure that the fact that you have volunteered to take a polygraph test is specifically included in your written statement.

Can I Have My Lawyer Present While I am Taking the Polygraph Test?

The police are under no obligation to allow your lawyer to be present while you take a polygraph and are very unlikely to do so.

However, if you are a child or have an intellectual disability, you should raise this and ask for an appropriate adult to be present.

Can I Choose to Answer Only Some Questions and Not Others?

You have a right against self-incrimination, meaning you are not required to say anything that could suggest that you are guilty of an offence. So in theory, yes, you can choose to answer some questions and not others.

However, you should bear in mind the purpose of the polygraph test. It is not to gather evidence to use against you, as with the statement-taking process. It is just for the police to form an impression of your honesty and innocence.

If you decline to answer some questions during a polygraph, the impression formed of your innocence will certainly be a negative one and you will have failed to achieve the only possible objective you could have in taking the polygraph test: showing that you have nothing to hide.

Therefore if you think you might need to decline to answer any question that is likely to be asked during a polygraph test, you may be better off declining to take the test altogether. You should seek legal advice on this issue if it’s relevant to you.

Can I Get a Copy of the Results of the Polygraph Test?

The police are not legally required to provide you with a copy of the results of the polygraph test. While you can certainly ask for it, they are unlikely to accede to your request. Given that the results are inadmissible in court, they are unlikely to be of much use to you in any case.

While the answers above should be helpful in reaching your decision, there is really no substitute for legal advice on this issue that takes into account your specific circumstances. Remember that any conversation you have with a lawyer about this issue is privileged and you don’t need to tell anyone what was discussed.

Good criminal lawyers can usually make themselves available at short notice to have a short discussion about issues like this by phone. Don’t be afraid to arrange a phone call with one to make sure you are doing everything you can to protect your interests.

Arrest and Investigation
  1. Police Investigation Process in Singapore
  2. When Can the Police Arrest Someone?: Arrestable and Non-Arrestable Offences in Singapore
  3. Police Arrest Procedure in Singapore
  4. Can a Civilian Arrest a Criminal in Singapore?
  5. Is Lying to the Police or Authorities an Offence in Singapore?
  6. Surrender of Passport to the Police and How to Get It Back
  7. What to Do If You’re Being Investigated for a Criminal Offence in Singapore
  8. Can You Say No to a Lie Detector Test in Singapore? And Other FAQs
  9. What Should You Do If You Witness a Crime in Singapore?
  10. Do You Have a "Right to Remain Silent" to the Police in Singapore?
  11. Extradition: What If You Flee after Committing Crime in Singapore?
  12. Warrant of Arrest: What to Do If It is Issued Against You in Singapore
  13. Search Warrant: The Issuance and Execution of It in Singapore
  14. Police Custody in Singapore: What You Should Know
  1. The Essential Guide to Bail and Personal Bonds in Singapore
  1. Magistrate’s Complaints, Private Summons and Private Prosecutions in Singapore
  2. Prosecutorial Discretion in Singapore
  3. What is Private Prosecution?
  4. Compounding or Composition of Offences in Singapore
  5. Criminal Records in Singapore
  6. Plea Bargaining in Singapore: All You Need to Know
Criminal Proceedings
  1. Compensation for Crime Victims in Singapore: How to Obtain
  2. Exercising Your Right to Self-Defence When Attacked in Singapore
  3. Claiming Trial as an Accused
  4. Mitigation Plea
  5. Pleading Guilty in Singapore: Consequences & Withdrawal of Plea
  6. Guide to Filing a Criminal Appeal in Singapore
  7. Presidential Clemency in Singapore
  8. Probation: Eligibility and Whether It Leaves a Criminal Record
  9. Reformative Training in Singapore: When Will It be Ordered?
  10. Visiting a Loved One in Prison or On Death Row in Singapore
  11. 7 Detention Orders in Singapore and When Will They be Ordered?
  12. Consequences of Receiving a Stern Warning in Singapore
  13. Are You Eligible for a Mandatory Treatment Order (MTO)?
  14. Can I Represent Myself in a Criminal Court Case in Singapore and How?
  15. Caning in Singapore: Judicial, School & Parental Corporal Punishment
  16. Criminal Motion: What is It and How to File One in Singapore
  17. Getting Parole (Early Prison Release) in Singapore
  18. Repatriation or Deportation from Singapore: How Does It Work?
  19. How Can Adult Offenders Get Probation in Singapore?
Sexual Offences
  1. Legal Age for Sex in Singapore and Common Sexual Offences
  2. Accused of Molest: Outrage of Modesty in Singapore
  3. What Can Victims of Sexual Harassment in Singapore Do?
  4. What is the Law on Sexting in Singapore?
  5. Revenge Porn: What If Your Nudes are Leaked in Singapore?
  6. Crime of Voyeurism in Singapore (Penalties and Defences)
  7. Consent in Sexual Offences in Singapore and What Victims Can Do
  8. STDs: Can I Go to the Police If a Partner Infected Me in Singapore?
  9. Child Pornography in Singapore: Offences and Penalties
Vice-Related Offences
  1. Is it illegal to visit prostitutes in Singapore?
  2. Is Watching, Downloading or Filming Porn Illegal in Singapore?
  3. Singapore's Drug Laws: Possession, Consumption and Trafficking
  4. When Can You Legally Gamble (In Public or Online) in Singapore?
  5. Is Vaping Illegal in Singapore?
  6. DUI: Here are the Penalties for Drink-Driving in Singapore
  7. Legal Drinking Age in Singapore and Other Drinking-Related Laws
  8. Singapore's Legal Smoking Age and Common Smoking Offences
  9. The Offence of Human Trafficking in Singapore and Its Penalties
  1. Penalties for Cheating/Scamming and What Victims Can Do
White-Collar Crimes
  1. Criminal Breach of Trust (CBT) in Singapore: Elements and Penalties
  2. Dishonest assistance and knowing receipt - The case of David Rasif
  3. Anti-Money Laundering Laws and You
  4. All You Need to Know About Corruption in Singapore
  5. 5 Things You Need to Know about Insider Trading
Other Criminal Offences
  1. Murder vs Culpable Homicide in Singapore: Differences & Penalties
  2. Is Suicide Illegal in Singapore? Will I Be Punished for Trying?
  3. Is it illegal to feed stray animals in Singapore?
  4. Criminal Intimidation: Penalties for Making Threats in Singapore
  5. Penalties for Impersonating Someone and Victim Redress
  6. What are Sham Marriages and Are They Illegal in Singapore?
  7. Public Assemblies and Processions in Singapore: Police Permits and the Public Order Act
  8. Racial Enmity: Sections 298 and 298A Penal Code Explained
  9. Penalties for Unlawful Assembly and Rioting in Singapore
  10. Voluntarily Causing Hurt Penalties in Singapore (Non-Arrestable)
  11. Misbehaving in Public: 5 Things You Need to Know
  12. Is it Legal for Drivers to Carpool in Singapore?
  13. Complete Guide to E-Scooter and PMD Laws for Singapore Riders
  14. Is Joining a Gang Illegal in Singapore?: Being Recruited and Penalties
  15. What Happens If You’re Caught Speeding in Singapore?
  16. Charged with a Traffic Offence in Singapore: What to Do
  17. Penalties for Committing Theft in Singapore
  18. Road Rage: What is It and How are Offenders Sentenced in Singapore
  19. Singapore Fake News Laws: Guide to POFMA (Protection from Online Falsehoods and Manipulation Act)
  20. Laws and Penalties for Doxxing in Singapore (With Examples)
  21. Littering and Killer Litter Offences: Here are the Penalties in Singapore
  22. Organised Crimes: Penalties/Orders Syndicates Face in Singapore
  23. Animal Cruelty in Singapore: Offences, Penalties & How to Report
  24. Penalties for Dishonest Misappropriation of Property in Singapore
  25. Penalties for Financing Terrorist Operations in Singapore
  26. Penalties for Illegal Immigration and Overstaying in Singapore
  27. Kidnapping Scam: Penalties & Responding to a ‘Kidnap Call/Text'
  28. Religious Cults in Singapore: Are they Illegal? Penalties & More
Certificate of Clearance
  1. How Do You Apply for a Certificate of Clearance in Singapore?