How does a payphone knows when you put $1 coin?

Question

How does a payphone knows when you put $1 coin?

Answer 1

There's a little man in there with a magnet and he knows that if you put a washer or something made of iron it will stick to the magnet,if it gets past the magnet ok he weighs it and if it weighs exactly the same as a $1 coin it then gets an optical inspection, a light is shone on it and the reflection is measured (a pixel count)and compared to the stored data of a real $1 coin,if all this is ok you may make your phone call,LOL.

Answer 2

Weight. Same way it knows a american quarter from a canadian one. american quarters weigh 2.5 ounces. a canadian quarter weighs 2.35 ounces. the canadian coin is worth 23.5 american cents (C The Pattern?)

Answer 3

There are a series of tumblers in the coin slot that sense the size of the coin and also anti-tampering ones to judge thickness to account for fakes.  It then sends audible sounds through the receiver to the phone company to count the coins.  In some phones you can hear the tones.  It works in a similar way to the touchtones that you hear when you press the numbers.