From Consumer Wiki
When a body guard is hired to protect a single individual and provides protection or security for one employer, is listed on the payroll of that employer, whose wages are paid directly by that employer, and who solely works for that employer and does not carry a baton or firearm, he/she is considered an "in-house security guard." It is not necessary for an in-house security guard to register as a security guard with BSIS, but he/she may do so.
If he/she wants to carry a firearm or baton, he/she must be licensed with the California Department of Consumer Affairs, Bureau of Security and Investigative Services as a guard and have a valid firearm or baton permit. The person must pass the "powers to arrest" examination and send in a fingerprint card to be reviewed by the California Department of Justice.
If an individual hires out body guards through his/her own business, that person must be registered as a private patrol operator.
Bureau of Security and Investigative Services
Publications available: Security and Investigative Services, (Bureau of)
See other: Security and Investigative Services, (Bureau of) fact sheet
Other referrals: Firearms/Guns