How does a vending machine tell the difference between coins?

Similarly one may ask, how do vending machines check coins?

Some vending machines use ultraviolet scanners tomeasure the glow from a bill to verify it is real. Real currencybills are also printed using magnetic ink. Many vendingmachines also use a magnetic reader to detect the magneticsignature of a bill to ensure it's real and determine itsdenomination.

Similarly, does a coin on a string work? Characters inserting a tied coin into acoin-operated device and then pulling the coin outwith the string to get a free item or service from themachine. In modern times, coin-operated machines simply havea one-way ratchet, preventing the return of any coin once ithas passed the counting mechanism.

Similarly one may ask, do fake bills work in vending machines?

Instead of magnetic heads, they use photocells to detectthe various shades of ink on a given bill. They read thedifference in ink on the bills you put into the vendingmachine and are able to determine if the bill isfake and what denomination it is.

Do vending machines charge extra for credit cards?

In fact, it's a common occurrence for many creditor debit card transactions and not just limited tovending machines. The charge you see is called anauthorization hold, a well-known practice within the bankingindustry.