Cipher Devices are designed to make codes unreadable to anyone but the person meant to receive it. This is usually done by switching letters and numbers with other letters to making it look like a jumbled up mess of letters and numbers to anyone who reads it.
In 1934, a man named Boris Hegelian invented a cipher machine for the french secret service. During World War II, over 14,000 of the machines were made for the U.S.
Today, cipher devices are still being used. The most simple one used is made of two wheels, one inside another.
Others are more complicated, using 25 or more whhiles to make a cipher.