I was talking to a customer the other day as I ink-checked her 50 dollar bill. She said that she was a convience store manager and that she always has to check for fake bills. She then said something along the lines " And you gotta be careful, because people will put the 20 dollar strip in a 5 dollar bill"
I then thought to myself, thats stupid. There is no way that would work. But then I thought, well, how do they tell what currency you are putting in.
So, without meaning to incourage breaking the law, how do money machines (the ones you can use at the grocery to checkout your own food) tell what currency you are putting in?
I’ve never seen such a machine (specifically) but I imagine that they work the same way as other currency-counting devices.
It depends from machine to machine (and from country to country,) but they usually employ a combination of optical and magnetic sensors.
In the U.S. and Canada, at least, the bills are usually scanned with both UV scanning and magnetic scanning.
(The magnetic scanning isn’t like a credit card swipe, obviously, but different patterns of magnetic material for different denominations. The information is in where they are physically on the bill, not stuff recorded onto a magnetic medium.)
I can’t imagine any way that someone might put a specific portion of one bill into a bill of another denomination that would fool a reasonably sophisticated machine or human being.