Law Enforcement Availability Pay is, per the United States Office of Personnel Management, a type of premium pay that is paid to Federal law enforcement officers who are criminal investigator

Detective

A detective is an investigator, either a member of a police agency or a private person. The latter may be known as private investigators or "private eyes"...

s. Due to the nature of their work, criminal investigators are required to work, or be available to work, substantial amounts of "unscheduled duty." Availability pay is generally an entitlement

Entitlement

An entitlement is a guarantee of access to benefits based on established rights or by legislation. A "right" is itself an entitlement associated with a moral or social principle, such that an "entitlement" is a provision made in accordance with legal framework of a society...

 that an agency must provide if the required conditions are met, but is optional in any agency's Office of the Inspector General

Office of the Inspector General

Office of the Inspector General is an office that is part of Cabinet departments and independent agencies of the United States federal government as well as some state and local governments. Each office includes an Inspector General and employees charged with identifying, auditing, and...

that may employ fewer than five criminal investigators.