Under California law, a polygraph test is not admissible in court unless all parties agree to admit it into evidence. Police and employers cannot force a suspect, witness or employee to take a polygraph. Most attorneys would advise that you should never submit to a police or employer polygraph without the guidance of your own legal counsel.
A polygraph test is when a polygraph examiner asks you questions to determine if you are telling the truth. The test is also known as a lie detector test. The test is given to defendants and/or witnesses in criminal cases and sometimes to employees as a condition of employment.
A polygraph is an electrical device that measures your biological changes when you answer questions. These changes can indicate when you are more prone to telling the truth or stating a lie.
Studies have shown that lie detector tests are not reliable all of the time. Because of this, test results are not admissible as evidence in a jury trial. This is unless the prosecutor and the defense attorney agree to have the results admitted.
Note that employers are generally prohibited from using these tests on employees. This comes from both:
- California law, and
- federal law.
If you are suspected of a crime, you should not take these tests unless you first speak with a criminal defense attorney.
Note, though, that you can do a private polygraph test to prove you are innocent.
A private polygraph test is when you hire a polygrapher and voluntarily take a lie detector test in order to demonstrate that you are being truthful about a matter. This is frequently done in criminal cases to exonerate you.
Our California criminal defense attorneys will highlight the following in this article:
- 1. Is a polygraph test admissible in court in California?
- 2. Can an employer ask or require me to take a polygraph test?
- 3. Should I take a lie detector test if asked to do so by the police?
- 4. Can I fail a lie detector test even if I am telling the truth?
- 5. Can I do a private polygraph to prove I am innocent?
1. Is a polygraph test admissible in court in California?
California law holds that the results of a polygraph test can only be admitted into evidence in a limited situation.
This situation is when both the prosecution and defense agree as to the admission of the results. “Admitted into evidence” means the results can be shown to a jury or judge.
Example: Jerome is charged with grand theft auto, per Penal Code 487d1 PC. He has a solid alibi and says he is innocent of the crime from the moment he is arrested. He agrees to take a lie detector test to show his innocence. The test results show that he is truthful in saying he did not commit the crime. Here, these results can only be admitted into evidence, in front of a jury, if both Jerome’s attorney and the prosecutor agree on it.
An agreement must also take place before the following can be admitted into evidence:
- the opinion of a polygraph examiner,
- the fact that you offered to take a polygraph test,
- the fact that you refused or failed a test, and
- the fact that you took a polygraph test.1
2. Can an employer ask or require me to take a polygraph test?
In California, the law says that a private employer cannot subject an employee or a job candidate to a lie detector test.2
This holds true no matter if the test is administered as a condition of:
- employment, or
- continued employment.
Note, however, that an employer may still ask you to take a lie detector test. This is provided that you are:
- first advised of your rights, and
- this is done prior to the polygraph test.3
If done, and you agree, the employer can perform a test.
Note also that federal law prohibits employers from subjecting you to polygraph tests.4
3. Should I take a lie detector test if asked to do so by the police?
You should not take a lie detector test without consulting with a criminal defense lawyer. This is because these tests are not 100% reliable. Even though the results of the test are not admissible in court, it may not be in your interest to submit to a test.
You may “pass” a polygraph if the test indicates you are being truthful in denying you committed the crime. Even so, this does not give you the right to introduce the test results as exculpatory evidence in court. The Supreme Court has ruled that you do not:
- have a constitutional right,
- to introduce lie detector results into evidence.5
The court made this ruling even though the U.S. Constitution says you have a right to present a defense.6
Further, if you do take a test and fail, this makes it more likely police and prosecutors will view you as factually guilty, and thus charge you with the crime.
4. Can I fail a lie detector test even if I am telling the truth?
You can fail a polygraph test even if you are telling the truth.
A polygraph test does not measure whether you are lying. Rather, it measures the signs that suggest that you are lying.
During the test, an examiner asks you a series of questions.
A machine then records physiological changes in you as you answer. These include changes in:
- breathing rates,
- blood pressure, and
The idea behind these tests is that:
- if you tell the truth, you will not exhibit changes in these conditions, but
- if you lie, you will show changes.
Note though that these tests can cause you to experience a great deal of stress. This is especially true if you are asked detailed questions about:
- a particular crime, or
- an event at work.
This stress alone can lead to fluctuations in your physiological conditions. Fluctuations mean that you can show signs of lying even though you are telling the truth.7
5. Can I do a private polygraph to prove I am innocent?
You can do a private polygraph to prove you are innocent.
A private polygraph test is when a private polygraph examiner conducts a lie detector test. The test is given to defendants and/or witnesses in criminal cases.
The tests are considered “private” because you are not obligated to tell the prosecutor or authorities that the test is taken.
The examiner asks you whether you committed the crime. If you answer no and the test indicates truthfulness, these results can be given to the prosecutor in the hopes of getting the case dismissed. If the polygraph indicates you are being untruthful, then the test and the results are kept secret.
The tests are used in cases involving either misdemeanor or felony offenses.
It might be strategic for you to take a private polygraph in three situations. These are when it is used to:
- try and dismiss a charge during the pretrial process,
- persuade a prosecutor to agree to use a second test at trial, and
- convince you to enter into a plea bargain, or plead no contest.8
Trained polygraph examiners administer lie detector tests for a fee. The typical cost is between $200 and $2,000.
For additional help…
For additional guidance or to discuss your case with a criminal defense attorney, we invite you to contact us at Shouse Law Group.
- California Evidence Code 351.1 EC. See, for example, In re. Jordan R. (
- California Labor Code 432.2 LC.
- See same.
- See the Employee Polygraph Protection Act of 1988 (EPPA).
- United States v. Scheffer (1998), 523 US 303.
- See Sixth Amendment to the U.S. Constitution.
- The Truth About Lie Detectors (aka Polygraph Tests), American Psychological Association.
- See, for example, In re Kenneth H. (