Question Radar detectors are: Answers Encouraged to be used by drivers of CMVs. Allowed in CMVs that are not carrying passengers. Not permitted to be used by drivers under the age of 21. Prohibited. Explanation Illinois law prohibits the use of radar detectors by drivers of CMVs. Violation of this law is a petty offense with a minimum fine of $50 for a first offense and a minimum of fine of $100 for any subsequent offense.