The currency detectors in vending machines is a device that determines whether banknotes or coins are real or fake. These devices are used in many modern automated vending machines.
The Science Channel explains how vending machines detect coin values, ignore fakes, and prevent hanging snacks. This machine can decipher coins with pinpoint accuracy. Light sensors measure the size while electromagnets detect the metal type of the coin.
Take a look inside the inner workings of a vending machine in the video below.