A private investigator or PI is a person who undertakes investigations. Private investigators often work for attorneys in civil cases or on behalf of a defense attorney. Many work for insurance companies to resolve claims. Before the advent of no-fault divorce, many private investigators were hired to search out evidence of adultery or other illegal conduct within marriage to establish grounds for a divorce. Despite the lack of legal necessity for such evidence any more, according to press reports collecting evidence of adultery or other "bad behaviour" by spouses and partners is still one of the most profitable activities investigators undertake.
Private investigators have frequently been found in fiction; perhaps the most famous of these is the Sherlock Holmes character created by Arthur Conan Doyle, who would refer to himself in the jargon of his age as a "private inquiries agent." (See Crime fiction for details.)
Private investigators are licensed by the jurisdiction in which they work and may or may not carry firearms depending on local laws. Some are ex-police officers. Private investigators are expected to keep detailed notes and to be prepared to testify in court regarding any of their observations on behalf of their clients. Private investigators are often required to take great care to remain within the law (for example, being forbidden to trespass on private property or break into homes) on pain of losing their licenses as well as facing criminal charges.
see security guard