California Polygraph Law

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. And most attorneys would advise that a suspect should never submit to a police or employer polygraph without the guidance of their own legal counsel. 

A polygraph test is when a polygraph examiner asks a person questions to determine if he/she is 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 biological changes in people when they answer questions. These changes can indicate when someone is 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.

Suspects should not take these tests unless they first speak with a criminal defense attorney.

Note, though, that defendants can do a private polygraph test to prove they are innocent.

A private polygraph test is when a person hires a polygrapher and voluntarily takes a lie detector test in order to demonstrate that he or she is being truthful about a matter. This is frequently done in criminal cases to exonerate a defendant.

The tests are used in cases involving either misdemeanor or felony offenses.

Our California criminal defense attorneys will highlight the following in this article:

california polygraph test
Studies have shown that lie detector tests are not reliable all of the time.

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:

  1. the opinion of a polygraph examiner,
  2. the fact that the defendant (or a witness) offered to take a polygraph test,
  3. the fact that the accused (or a witness) refused or failed a test, and
  4. the fact that a party took a polygraph test.

2. Can an employer ask or require an employee 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.1

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 an employee to take a lie detector test. This is provided that the employee is:

  1. first advised of his/her rights, and
  2. this is done prior to the polygraph test.2

If done, and the employee agrees, the employer can perform a test.

Note also that federal law prohibits employers from subjecting employees to polygraph tests.3

Civil service rules prohibit the same with regard to government employees.

police speaking with person
You should not not a lie detector test without first speaking with a criminal defense attorney.

3. Should a person take a lie detector test if asked to do so by the police?

A person should not take a lie detector test without consulting with a criminal defense lawyer. This is because these tests are not 100% reliable. And even though the results of the test are not admissible in court, it may not be in a suspect's interest to submit to a test.

A suspect may "pass" a polygraph if the test indicates he is being truthful in denying he committed the crime. Even so, this does not give him the right to introduce the test results as exculpatory evidence in court. The Supreme Court has ruled that an accused does not:

  • have a constitutional right,
  • to introduce lie detector results into evidence.4

The court made this ruling even though the U.S. Constitution says a defendant has a right to present a defense.5

Further, if a person does take a test and fails, this makes it more likely police and prosecutors will view him as factually guilty, and thus charge him with the crime.

4. Can a person fail a lie detector test even if he/she is telling the truth?

A person can fail a polygraph test even if he/she is telling the truth.

A polygraph test does not measure whether a person is lying. Rather, it measures the signs that suggest that a person is lying.

During the test, an examiner asks a person a series of questions.

A machine then records physiological changes in the person answering. These include changes in:

  • breathing rates,
  • pulse,
  • blood pressure, and
  • perspiration.

The idea behind these tests is that:

  • a person telling the truth will not exhibit changes in these conditions, but
  • a person lying will show changes.

Note though that these tests can cause a subject to experience a great deal of stress. This is especially true if the person is asked detailed questions about:

  1. a particular crime, or
  2. an event at work.

This stress alone can lead to fluctuations in a person's physiological conditions. Fluctuations mean that a person can show signs of lying even though he/she is telling the truth.

5. Can defendants do a private polygraph to prove they are innocent?

Defendants can do a private polygraph to prove they 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 the defendant is not obligated to tell the prosecutor or authorities that the test is taken.

The examiner asks subjects whether they committed the crime. If they 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 the subject is 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 a defendant to take a private polygraph in three situations. These are when it is used to:

  1. try and dismiss a charge during the pretrial process,
  2. persuade a prosecutor to agree to use a second test at trial, and
  3. convince the defendant to enter into a plea bargain, or plead no contest.

Trained polygraph examiners administer lie detector tests for a fee. The typical cost is between $200 and $2,000.

For additional help...

california criminal defense attorneys
Call us for help at (855) LAW-FIRM

For additional guidance or to discuss your case with a criminal defense attorney, we invite you to contact us at Shouse Law Group.

Legal References:

Free attorney consultations...

The attorneys at Shouse Law Group bring more than 100 years collective experience fighting for individuals. We're ready to fight for you. Call us 24 hours a day, 365 days a year at 855-LAW-FIRM for a free case evaluation.

Regain peace of mind...

Shouse Law Defense Group has multiple locations throughout California. Click Office Locations to find out which office is right for you.

Office Locations

Shouse Law Group has multiple locations all across California, Nevada, and Colorado. Click Office Locations to find out which office is right for you.

Call us 24/7 (855) 396-0370