Private investigators, also known as private detectives or PIs, are hired professionals used for multiple purposes. Although PIs are not police officers, many have a criminal justice background. Many have developed their expertise on the job. PIs will work for private individuals or companies. Attorneys may hire detectives to build information for a case. A private detective provides investigative services, surveillance and background checks. Investigators use their skills to gather information on behalf of individuals, law firms and companies. In Pennsylvania, you are also required to be licensed as a PI to offer guard or other physical security services .