A private investigator or private detective is a person who secretly follows and observes persons in public places for the purpose of witnessing behavior and collecting evidence of any illegal or improper activities (photos, videos, etc.). During the divorce process a spouse who suspects their spouse of cheating (adultery) or other improper or illegal behavior may hire a private investigator to follow or “tail” the other spouse.

In California, private investigators are regulated under the Bureau of Security and Investigative Services (BSIS). They must be licensed to legally operate as private investigators in the state. The licensing process includes passing a criminal background check, having a certain amount of experience or education in the field, and passing a state-administered exam. When hired during a divorce process to investigate a spouse for potential cheating or other improper behavior, private investigators are allowed to observe and collect evidence in public places. However, they must conduct their activities within the bounds of the law, which means respecting privacy laws and not engaging in illegal activities such as trespassing, harassment, or wiretapping without consent. Evidence gathered by private investigators can be used in court, but it must be obtained legally to be admissible. It's important to note that while California is a no-fault divorce state, meaning that the court does not require proof of wrongdoing to grant a divorce, evidence of adultery or other misconduct may still be relevant for issues like spousal support or the division of marital assets.