Except as provided in subsection (b) of this section, an individual described in § 25–201(a) of this subtitle is a member of the Correctional Officers’ Retirement System as a condition of employment. Subject to paragraph (3) of this subsection, membership in the Correctional Officers’ Retirement System is optional for an individual described in § 25–201 of this subtitle who was employed by a participating governmental unit as a local detention center officer on the effective date of participation on or after July 1, 2006, but before July 1, 2017, for that participating governmental unit and who elects membership within 6 months of the effective date of participation. Subject to paragraph (3) of this subsection, membership in the Correctional Officers’ Retirement System is optional for an individual: described in § 25–201 of this subtitle who was employed by a participating governmental unit as a local detention center officer on the effective date of participation on or after July 1, 2017, for that participating governmental unit; and who elects membership before the effective date of participation. To elect to be a member of the Correctional Officers’ Retirement System, an individual shall file a written application with the State Retirement Agency on a form that the State Retirement Agency provides. An election to join the Correctional Officers’ Retirement System under this subsection is a one–time, irrevocable election. If an individual does not elect membership during the applicable period specified under paragraph (1) or (2) of this subsection, the individual may not subsequently become a member of the Correctional Officers’ Retirement System.