Editing Blue box (section)

===Technology===
It was technically possible to generate the tones with the technology available at the time the system was first deployed. A [[piano]] or [[electronic organ]] had keys that were close enough in frequency to work. With tuning, they could even be made dead on frequency. For dialing the phone number, the user would press two keys at a time. An experienced pianist might have found the key combinations awkward to play. But a blank [[player piano]] [[piano roll|roll]] could have been punched to operate the required keys and dial a phone number. Another strategy would have been to purchase [[doorbell]]s, remove the plungers, and mount them on a frame that could be set over the piano keyboard. Twelve DPDT pushbuttons, labelled KP, ST and the 10 digits, would operate pairs of plungers to play the phone company tones, after the E7 piano key had been pressed and released.

At the time, there were consumer devices for recording on wire or blank [[phonograph record]]s, so the piano did not have to be near the phone. Consumer [[tape recorder]]s came later and made the recording process easier. Small, [[Electric battery|battery]] powered, tape recorders allowed the tones to be played back almost anywhere.

It was possible to construct an electronic blue box with 1940s [[vacuum tube]] technology, but the device would have been relatively large and power hungry. Just as it did for radios, shrinking them from the size of toasters to the size of cigarette packages and allowing them to be powered by small batteries, transistor technology made a small, battery powered, electronic blue box practical.

AT&T security captured its first blue box in about 1962, but it probably was not the first one built.

A typical blue box had 13 pushbuttons. One button would be for the 2600{{nbs}}Hz tone, pressed and released to disconnect the outgoing connection and then connect a digit receiver. There would be a KP button, to be pressed next, 10 buttons for telephone number digits, and the ST button to be pressed last. The blue box may have had 7 oscillators, 6 for the 2 out of 6 digit code and one for the 2600{{nbs}}Hz tone, or 2 oscillators with switchable frequencies.

The blue box was thought to be a sophisticated electronic device and sold on the black market for a typical $800–1,000 or as much as $3,500. Actually, designing and building one was within the capabilities of many electronics students and engineers with knowledge of the required tones, using published designs for electronic oscillators, amplifiers and switch matrixes, and assembled with readily available parts. Furthermore, it was possible to generate the required tones using consumer products or lab test equipment. The tones could be recorded on small, battery powered, cassette recorders for playback anywhere. In the early 1980s, [[Radio Shack]] sold<ref>{{cite web | url=https://www.radioshackcatalogs.com/flipbook/1984_radioshack_catalog.html | title=1984 Radio Shack Catalog }}</ref> pairs of [[Intersil ICL8038]] voltage-controlled oscillator chips which were ideal for the purpose.  A common hack was to use a TI-30 [[Calculator#Pocket calculators|pocket calculator]] as the chassis of the device, with the diodes for the switch matrix wired into the keypad.  A miniature audio jack connected through the recharge port for the calculator's optional rechargeable battery would then be used to connect the speaker to play the tones into the handset.

To reduce call setup time, telephone numbers were transmitted from machine to machine in a "speed dial" format, about 1.5 seconds for a 10-digit number, including KP and ST. To catch the cheaters, AT&T could have connected monitors to digit receivers that were not being used for operator dialed calls and logged calls dialed at manual speed. So, some hackers went to the extra trouble of building blue boxes that stored telephone numbers and played the tones with the same timing as the machines.