Lie detector – Definition, legal significance, and application
Term Explanation: Lie Detector
A lie detector, also known as a polygraph, is a technical device designed to detect falsehoods by measuring physiological responses. The parameters measured include, among others, blood pressure, pulse rate, skin conductivity, and respiration. The lie detector is based on the assumption that certain physical reactions intensify when making untruthful statements.
How a Lie Detector Works
The polygraph process uses electrodes and sensors to record a test subject’s physical responses to previously established questions. The evaluation is based on characteristic changes in the recorded biological values. These changes may, but do not necessarily, indicate a lie. Nervousness, stress, or anxiety can also cause similar patterns.
Legal Classification of the Lie Detector in Germany
Use in Criminal Proceedings
In Germany, the use of lie detectors in criminal proceedings is highly controversial and is largely rejected. According to consistent case law of the Federal Court of Justice (BGH), the use of a polygraph test as evidence is generally inadmissible. The main reasons for this are the lack of scientific reliability of the procedure and the significant risks to the free will of the person tested.
Protection Against Self-Incrimination and Lie Detector Test
A significant legal aspect is the prohibition of compulsion to self-incriminate, derived from the principle ‘nemo tenetur se ipsum accusare’. This principle is enshrined in Art. 1 Basic Law in conjunction with Art. 2 para. 1 Basic Law and Art. 6 para. 1 ECHR. It protects the accused from being forced to disclose incriminating information by participating in a lie detector test.
Personal Rights and Voluntariness
The administration of a lie detector test directly interferes with personal rights. A prerequisite for legally secure application would always be the voluntary and informed consent of the person concerned. However, there are doubts as to whether a truly free decision of will can always be guaranteed under criminal procedure conditions.
Evidentiary Value and Exclusion from Admissible Evidence
Because of the disputed scientific foundation, the results of a lie detector test are not recognized as admissible evidence in criminal proceedings. This applies to both incriminating and exculpatory results. Even if the test subject voluntarily consents, the exclusion from admissible evidence is not generally waived.
Lie Detector in Civil Law
Use in Employment Law
In employment law, the lie detector is rarely used, for example in internal investigations. Here too, there are significant doubts regarding voluntariness and the reliability of the method. Participation in a polygraph test must not be a condition for entering into or maintaining an employment relationship. Other uses may trigger data protection and personal rights conflicts.
Data Protection and Personal Rights
Polygraph assessments collect highly personal data. According to the provisions of the General Data Protection Regulation (GDPR) and the Federal Data Protection Act (BDSG), the processing of such data is only permitted under very strict conditions. The requirements for consent under Art. 7 GDPR are particularly strict in this context. Misuse or forced use can give rise to claims for injunctive relief, removal, and damages under civil law.
International Legal Comparison: Lie Detector Test
Legal Treatment Abroad
The acceptance and use of lie detectors varies greatly internationally. While in the USA polygraphs are partly used as investigative and evidentiary tools, they are legally excluded in many European countries, including Germany. There is also differentiated case law in the USA regarding individual states and the role of voluntary consent.
European Convention on Human Rights (ECHR)
The use of lie detectors touches on the rights protected in Art. 8 ECHR regarding respect for private and family life. Any application by European or national authorities is subject to strict requirements of permissibility, proportionality, and voluntariness.
Lie Detector: Legal Risks and Limitations
Legal Risks of Use
The unlawful use of lie detectors can entail numerous risks:
- Criminal law risks: Coercive application or deception during the test may be classified as bodily harm or coercion.
- Civil law risks: Unauthorized evaluation or publication of test results may give rise to claims for injunctive relief and damages.
- Employment law risks: Discrimination, bullying, or dismissal based on a test may be unlawful and subject to challenge.
Limits of the Lie Detector under the Law
National and international standards draw clear boundaries for the use of the lie detector. From the perspective of the rule of law, scientific uncertainty about the method, fundamental rights risks, and protection of privacy outweigh the interest in objective truth-finding by technical means.
Conclusion: Legal Assessment of the Lie Detector
The lie detector is not a legally valid piece of evidence in Germany and is regarded in law as unreliable and associated with significant risks to fundamental rights. In both criminal and civil law, data protection, personal rights, and procedural concerns predominate. Only under strict conditions, especially with clear and documented voluntariness, is its use considered legally justifiable—and only outside court proceedings and without evidentiary value in court. Abuse or unlawful use can have far-reaching legal consequences.
See also
- Exclusion from Admissible Evidence
- Protection Against Self-Incrimination
- Fundamental Rights in Criminal Proceedings
- [Datenschutzrecht]
Frequently Asked Questions
Is the use of a lie detector permitted in court in Germany?
The use of a lie detector, also called a polygraph, is legally inadmissible in German court proceedings. A result obtained by a lie detector is, according to established case law of German courts, generally not admitted as evidence. This is primarily due to doubts about the scientific reliability of the polygraph procedure as well as the right to a fair and self-determined process. The results of a lie detector test could influence the court’s freedom of decision, without their evidentiary value being conclusively established. There is also a risk of self-incrimination, which is not permissible under Section 136 of the Code of Criminal Procedure. Even a voluntary consent by the accused does not automatically make the result admissible, as the courts do not recognize the procedure as court-proof.
What are the legal consequences of refusing to undergo a lie detector test?
There is no legal obligation in Germany for a defendant, witness, or party to submit to a lie detector test. No one can be forced to participate in a lie detector test under German law. Such refusal may not be held against the person concerned, as they are protected by the principle of nemo tenetur se ipsum accusare (no one is obliged to incriminate themselves). Therefore, no disadvantage may result from such refusal in court.
Can lie detector tests be used in employment law?
In the field of employment law, lie detector tests are also viewed extremely critically. The employer cannot base employment actions solely on the result of a lie detector test. Since the test must be voluntary and employment consequences for refusal are inadmissible, such results are regularly not used in employment law practice. In termination protection proceedings, the test result may under certain circumstances be considered as an indication, but due to its lack of evidentiary value and legal risks, it generally does not carry weight.
Are lie detector tests permitted in police investigations?
In investigations, the lie detector is used by the police at most as an informal, non-standardized tool for conducting interviews or to rule out major contradictions in a person’s statements. Use in police questioning requires the explicit, informed consent of the person concerned and may never be enforced. The results of such a test have no evidentiary value and may not be recorded as facts in investigation files or used in court.
How does the right to self-determination protect against the use of lie detectors?
German law protects personal freedom and the right to physical and mental self-determination. The use of a lie detector interferes with these fundamental rights, as the procedure relies on measuring bodily functions to which no one may be compelled. Therefore, such intervention always requires explicit, voluntary consent. Even if such consent is present, the legal usability of the results remains severely restricted, since the procedure is considered unreliable and there is a risk that the person being tested may be subject to pressure.
Are there national or international legal standards regarding the use of lie detectors?
There are no German or European legal standards that explicitly regulate or permit the use or exploitation of lie detector tests. Instead, general procedural principles—such as the right to a fair trial, protection against self-incrimination, and the right to physical integrity—are decisive. International documents, such as the European Convention on Human Rights, also protect the right to a fair and self-determined process and question the admissibility of the lie detector.
Can private lie detector tests outside court proceedings be legally problematic?
Even in the private sphere, lie detector tests are subject to legal requirements. They always require the informed, voluntary consent of the person concerned. A forced or non-consensual test may, under certain circumstances, have legal consequences such as claims for damages or injunctive relief. Regardless of voluntariness, the result has no legal significance and, in particular, may not be published or shared with employers, authorities, or third parties without consent.
