Mich. Comp. Laws § 338.1054

Sec. 4. The department may issue separate licenses to security alarm system contractors, private college security forces, private security police, and private security guard agencies. This section does not prevent a private detective or private investigator licensed under the professional investigator licensure act, 1965 PA 285, MCL 338.821 to 338.851, from performing the services of a private security guard or private security police except that a private security guard or private security police may not perform the services of a private detective or private investigator without obtaining a private detective or private investigator license.