a transparent - front vending machine includes an optical vend - sensing system with an article sensing subsystem arranged athwart a vend space . the article sensing subsystem has two emitter / detector arrays , each having at least one emitter and a plurality of detectors . the emitter / detector arrays are arranged so that at least some electromagnetic radiation emitted by an emitter of the first array can be detected by at least two active detectors of the second array , and at least some electromagnetic radiation emitted by an emitter of the second array can be detected by at least two active detectors of the first array so that articles falling through the vend space will interrupt electromagnetic radiation between an emitter and at least one detector . at least two emitters are active at one time .