Secret listening to conference between prisoner and his attorney

(a) It shall be unlawful for any person willfully to overhear, or procure any other person to overhear, or attempt to overhear any spoken words between a person who is in the physical custody of a law-enforcement agency or other public agency and such person's attorney, by using any electronic amplifying, transmitting, or recording device, or by any similar or other mechanical or electrical device or arrangement, without the consent or knowledge of all persons engaging in the conversation. (b) No evidence procured in violation of this section shall be admissible over objection against any person participating in such conference in any court in this State.