Detectives in California work within a specialized unit of the police department, investigating crimes. Detectives spend most of their time collecting and analyzing evidence, conducting interviews of witnesses and interrogating suspects and piecing together information to solve a crime. Requirements for detectives in California usually vary among city and local police departments, however most require a college degree, experience as a patrol officer, passing a written exam and accepting a transfer to a unit with a detective slot.

Work as a police officer. All departments in California usually require a detective to have anywhere from three to five years experience as a police officer, before he or she may transfer to or apply for a detective slot. Candidates will need to get hired as a police officer through the individual department's selection process, which usually includes passing a variety of tests that may include a written exam, physical-fitness test, medical check-up, psychological exam and graduation from the department's police academy. All departments have varying requirements and selection processes, therefore candidates must contact the department they want to work for and inquire.

Graduate with a college education while working as a police officer by attending classes while not at work or by taking distance education courses. Some detective units require candidates to have at least 60 hours of college credit, preferably in criminal justice or forensic science before they will consider an application. Other units may require all detectives to have a bachelor’s degree. Police officers should inquire within their individual department regarding requirements to become a detective.

Apply for an open position or request a transfer to an open detective slot. Most police departments seek to promote officers to detective internally, rather than seeking detectives from other forces. In order to transfer, most departments will request the officer to write a letter of intent and submit to the detective unit he or she intends on transferring. When a slot becomes available, the police may then undergo the selection process for detective, which usually requires passing a written exam, retaking the physical fitness and medical test and taking a psychological test. Upon completing and passing all tests according to the department and unit standards, the police officer may then be transferred.