625 ILCS 45/5-16b
If a law enforcement officer has reasonable suspicion to believe that a person is violating or has violated Section 5-16 or a similar provision of a local ordinance, the officer, prior to an arrest, may request the person to provide a sample of his or her breath for a preliminary breath screening test using a portable device approved by the Illinois State Police. The results of this preliminary breath screening test may be used by the law enforcement officer for the purpose of assisting with the determination of whether to require a chemical test as authorized under Section 5-16 and the appropriate type of test to request. Any chemical test authorized under Section 5-16 may be requested by the officer regardless of the result of the preliminary breath screening test if probable cause for an arrest exists. The result of a preliminary breath screening test may be used by the defendant as evidence in any administrative or court proceeding involving a violation of Section 5-16.
625 ILCS 45/5-16b