In the computer hacking scene of the 1980s, demon dialing was a technique by which a computer is used to repeatedly dial a number (usually to a crowded modem pool) in an attempt to gain access immediately after another user had hung up. The expansion of accessible internet service provider connectivity since that time more or less rendered the practice obsolete.
A similar technique was sometimes used to get the first call for prizes in radio "call-in" shows, thus leading to the adoption of random "fifth caller," "seventeenth caller" etc. by radio stations to circumvent this practice.
The term "demon dialing" derives from the Demon Dialer product from Zoom Telephonics, Inc., a telephone device produced in the 1980s which repeatedly dialed busy telephone numbers under control of an extension phone.[1]
"Demon dialing" is sometimes used as a synonym for war dialing, a related technique which uses automated computer modem dialing, though instead to conduct a random search to locate other modem-connected lines.
Automatic redial, which is essentially exactly the same thing, but for modems, and included in most telecommunications programs that use modems, including all variants of Dial-up networking ever included in the Windows operating system.