Dial tone decoder in criminal investigations
A dial tone decoder is a device used primarily in criminal investigations to decipher and record telephone numbers dialed from specific phones. It works by detecting the unique frequencies generated when numbers are pressed on a touch-tone keypad, allowing investigators to establish connections between individuals based on the calls made. This functionality is crucial for gathering information without accessing the content of conversations, as it employs a method known as a pen register tap. Such taps are difficult to detect and have historically been easier to obtain court orders for compared to traditional wiretaps, particularly after the implementation of the Patriot Act, which simplified the process for law enforcement.
However, the relevance of dial tone decoders has diminished in the 21st century due to the widespread practice of telecommunication companies recording call information for billing purposes. As a result, law enforcement can often obtain the necessary data directly from telecom providers without needing to resort to less effective methods like pen registers. Furthermore, with major telecom companies moving away from the technology associated with dial tone decoders, their use in investigations is anticipated to continue declining.
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Dial tone decoder in criminal investigations
DEFINITION: Device that deciphers all numbers dialed from a particular telephone and sends the information to an external recorder.
SIGNIFICANCE: During criminal and foreign intelligence investigations, information about what telephone numbers have been called from specific telephones can be important for establishing connections among individuals.
When a number key is pressed on a touch-tone telephone, two tones are generated. Each vertical column on the keypad generates a high-frequency tone, and each horizontal row produces a low-frequency tone. When the high- and low-frequency tones of any key are mixed, they produce a tone of unique frequency associated with that specific keypad number. A dial tone recorder deciphers these unique frequencies on an outgoing telephone line and uses the information to route the call to the correct receiving telephone.
When a dial tone decoder is connected to an external device, information about the number called can be recorded, so that a third party can tell what number has been dialed. This is called a pen register tap. The telephone conversation is not accessible to the third party, only the number called. A modern pen register tap usually sends the information to a computer with an infrared port (an infrared data association, or IRDA) that can communicate wirelessly with the dial tone decoder in the same way a remote control turns on a television. The presence of a pen register tap on a telephone line is difficult to detect.
Historically, wiretap laws in the United States were designed to protect the content of telephone conversations. Initiating a telephone wiretap required a court order and a high level of proof that the wiretap was essential to an investigation. Because pen register taps (or the reverse, trap and trace taps, which decipher the numbers of the telephones that originate incoming calls) do not allow access to the contents of calls, it has historically been much easier for investigators to obtain court orders for these types of taps. The Patriot Act, which was passed following the 2001 terrorist attacks on the Pentagon and the World Trade Center in New York City, made it even easier for law-enforcement agencies to place pen register taps. All the act requires is that the requesting agency certify that information likely to be obtained from the tap is relevant to an investigation.
In the twenty-first century, telecommunication companies routinely record originating and receiving telephone numbers of all calls for billing purposes, so pen register taps are not as useful as they once were. Law-enforcement agencies can get the same information by obtaining court orders that require telecommunication companies to release the calling information for particular individuals or telephones. As the use of dial tone continued to fall out of favor, with major telecom companies planning on discontinuing the techjnology in the early 2020s, dial tone decoders continued to decline in popularity with law enforcement agencies.
Bibliography
Bentley, Peter. "Why Your Phone's Dial Tone Could Soon Be Axed." BBC Science Focus, 26 June 2023, www.sciencefocus.com/science/why-do-we-still-have-dial-tones. Accessed 14 Aug. 2024.
Diffie, Whitfield, and Susan Landau. Privacy on the Line: The Politics of Wiretapping and Encryption. Cambridge, Mass.: MIT Press, 2007.
Olejniczak, Stephen P. Telecom for Dummies. Indianapolis, Ind.: Wiley, 2006.