Red box

Before cellular (radio) telephones became cheap and widely available, people who wanted to make telephone calls away from home typically used payphones. Older model payphones signalled the deposit of coins by ringing bells. A dime was represented by two dings, a nickel by one, and a quarter by a lower-pitched chime. For local calls, the phone would activate when the price of a local call (a nickel or a dime) was deposited. For long distance calls, an operator would listen to the bell chimes as coins were deposited, would record payment of the toll charge, and would then connect the call. With the advent of solid-state technology, bells were replaced by electronic tones. One beep was a nickel, two a dime, and five a quarter. This permitted completion of toll calls without operator intervention, because the tones could be detected by the automatic switching system at the telephone company.

Phone phreaks came up with methods to play these tones into the telephone's microphone, thus fooling the system into completing free calls. These methods included playing back the tones using an audio recorder (usually a tape recorder as magnetic tape was then the primary means of recording audio).

A red box is a phreaking device that synthesizes these tones, which are not unlike the DTMF tones used for dialing. Other devices which generated these tones included modified Radio Shack tone dialers, and Hallmark audio-recording greeting cards.

The specifications for the tones are as follows:

 RED BOX FREQS: 1700 HZ AND 2200 HZ MIXED TOGETHER

 A NICKEL IS 66 MS ON (1 BEEP).
 A DIME IS 66MS ON, 66MS OFF, 66MS ON (2 BEEPS)
 A QUARTER IS 33MS ON, 33MS OFF REPEATED 5 TIMES.
 (MS= MILLISECOND). 

Red boxes no longer work in most western nations, the pay phones either include filters on the handset to remove this sound, or in many cases, use digital systems that are not so easily fooled. The basic concept still works in many other countries, however.