Phone Phreaking "BLUE BOX" (circa 1975)

What is it?

This device is certainly one of the most unique pieces of electronic equipment that I have been able to collect so far. It is essentially a hacking tool disguised to look like a common 1970's Texas Instruments hand held electronic calculator. Basically a real calculator was sacrificed and modified to produce audio frequency signaling tones which allowed the user to freely (and illegally) access the Bell Telephone System long distance network. This was possible in the 1970's because the Bell System had been designed in the 1960's with a fatal flaw... it accepted both normal voice and control tone frequencies over the same circuit. Unfortunately the Bell System engineers hadn't anticipated the advances in electronics technology which eventually allowed the design and construction of control devices at home by ingenious hackers. The present telephone network is digitally operated so audio based devices such as the one described below are now useless.

The first clue that something unusual is going on is the earphone device on the left with a short plug in cable.

A look at the back and into the battery compartment still does not reveal anything out of the ordinary.

Folding the circuit board out confirms that this is no longer a functional calculator... the LED display panel is missing! A real TI Datamath circuit board is shown on the right for comparison. Date codes on the "blue box" IC's range from 7449 to 7515 which indicate that this device was probably made in mid 1975.

Here is a view of the back of the original TI keypad which has been rewired to the "blue box" tone generator circuit board. The large silver device is crystal for the audio frequency oscillator. Notice on the right side that the red plastic LED window has been covered with black electrical tape to help reduce external suspicion.

Several interesting articles are available on the web which describe phone phreaking and the associated hardware in more detail. One particularly good source is entitled "Secrets of the Little Blue Box". It was originally printed in the October 1971 issue of Esquire Magazine. Just type those keywords into a Google search and you will find plenty of reference material.

To operate this "blue box" a standard Bell Telephone earpiece was plugged into the calculator's AC adapter jack. Next the user would place the earpiece near the telephone handset mouthpiece and use the calculator keypad to enter the desired long distance trunk access codes as well as area codes and phone numbers. On this particular unit the "CE" key produced the 2,600 Hz trunk line control tone. The "+" and "=" keys also provided control tones. The ten digit keypad worked just like the one on a regular touchtone phone. In fact with this device you could turn your plain old rotary dial phone into an incredible touchtone super phone that could call almost any other telephone on the planet... for free.

This particular "blue box" came with a crudely typed set of instructions.

Final thoughts

To help put all this in perspective, consider the mood of the country, and particularly the baby boom generation towards the Bell Telephone System back in the 1970's. Long distance calls were relatively expensive and one had no choice but to use the Bell System to make them.  Bell (derogatorily referred to as "Ma Bell") was generally seen by college students as a huge uncaring and wealthy monopoly that deserved to be ripped off. Consequently Bell was an obvious target for attack by the young. Here is an ad from June, 1970 for a wall poster which expressed the popular youth culture attitude regarding the nation's only telephone company.

In addition to the sophisticated hardware hacking approach of the "blue box", it was also common to make free long distance calls using the much riskier method of creating fraudulent Bell Telephone credit card numbers. The following article actually appeared in my own college newspaper during my freshman year.

The origin of the name "blue box" was due to the fact the some of the earliest home built versions were actually housed in blue boxes. Below is a 1970's photo found on the web showing a happy phone phreak in action with such a device.

Returning to this particular "blue box"... someone or some group of enterprising hackers went to a lot of trouble to design and manufacture this cleverly disguised device. The external design was obviously intended to provide some degree of protection to the owner by deceiving the police or phone company investigators into thinking it was just a harmless calculator (as long as you didn't store the earpiece with the unit itself!). It is obviously not a single isolated home built unit, but instead appears to be one of many such devices which were illegally mass produced. Because of its underground nature, details of how this device was advertised, how many were made, how much it cost, etc. are difficult to find. If anyone reading this web page can provide any additional information regarding similar devices I would enjoy hearing from you.