How does a vending machines verify a dollar bill vs counterfeit?

Download this stock image: Hand feeding a five dollar bill into a slot machine

One time I was playing this coin pusher slot machine at my local Indian casino, when I noticed a big coin fall, but not be accounted for (up to

dollar bill slot machine Just put in a one dollar, 5 dollar, or twenty dollar bill in the slot very few casinos now have coins in, although a few do when you

dollar storm slot Slot machines include one or more currency detectors that validate the form of payment, whether coin, banknote, voucher, or token The machine pays out