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General Prohibition on Pen Register and Trap and Trace Device Use - 18 U.S.C. § 3121

Posted by Dmitry Gorin | Jan 31, 2024

Let's review the federal law, Title 18 U.S. Code 3121, a general prohibition on pen register and trap and trace device use; exception. Despite modern-day concerns about privacy in the digital age, the government has put some safeguards regarding how and when communications may be tracked. 

For example, under 18 U.S.C. 3121, it is a violation of federal law to use pen registers or trap and trace devices to track phone communications without specific authorization via a court order. 

Federal Prohibition on Trace Device Use - 18 U.S.C. § 3121
Using trace devices to track phone communications without authorization is a federal crime.

If you violate these rules and are convicted, you could face up to a year in federal prison. Plus, if you are under investigation and a government agency violates these rules to gather evidence against you, that evidence would be inadmissible in court.

18 U.S.C. 3121 says, “(a) In General, except as provided in this section, no person may install or use a pen register or a trap and trace device without first obtaining a court order under section 3123 of this title or under the Foreign Intelligence Surveillance Act of 1978 (50 U.S.C. 1801 et seq.) or an order from a foreign government that is subject to an executive agreement that the Attorney General has determined and certified to Congress satisfies section 2523.

(b) Exception. The prohibition of subsection (a) does not apply concerning the use of a pen register or a trap and trace device by a provider of electronic or wire communication service —

(1) relating to the operation, maintenance, and testing of a wire or electronic communication service or the protection of the rights or property of such provider, or to the protection of users of that service from abuse of service or unlawful use of service; or

(2) to record the fact that a wire or electronic communication was initiated or completed to protect such provider, another provider furnishing service toward the completion of the wire communication, or a user of that service from fraudulent, unlawful, or abusive use of service; or 

(3) where the user's consent of that service has been obtained.

(c) Limitation. A government agency authorized to install and use a pen register or trap and trace device under this chapter or State law shall use technology reasonably available to it that restricts the recording or decoding of electronic or other impulses to the dialing, routing, addressing, and signaling information utilized in the processing and transmitting of wire or electronic communications so as not to include the contents of any wire or electronic communications.

What Are These Devices?

Let's begin by discussing how pen registers, traps, and trace devices function. A pen register (a dialed number recorder or DNR) is a device or a program that records the numbers dialed from a specific telephone line. It doesn't record what is said during the call, but it keeps track of the phone numbers that someone dials out to. 

Law enforcement or other agencies can use this to track who a person is calling, whether from a mobile phone or a landline, where a pen registers outgoing data and a trap and trace device records incoming data. 

It is a tool used to capture incoming electronic or phone communication information. It records the number of incoming calls or Internet IP addresses of electronic communications to a particular line. 

Like a pen register, it doesn't record the contents of the communication (what is being said or the data being sent), but it keeps track of where the communications are coming from. Think of it as an advanced form of Caller ID.

Notably, these devices differ from a wiretap, which must be authorized under a separate law. While pen registers traps and trace devices track source-and-destination information only, a full-blown wiretap is a setup that can record the actual contents of telephone, email, or other oral communications. 

What Does the Law Say?

In general terms, under 18 U.S.C. 3121, you can't use a pen register or a trap and trace device on any phone line unless you get a special court order authorizing you to do so. 

The purpose behind this law is to enforce protections guaranteed by the Fourth Amendment, which safeguards people from privacy invasion and unlawful search and seizure. 

While data collected by these devices doesn't reveal the contents of the conversation, the data itself is still protected from search and seizure unless there is probable cause—hence the need for a court order.

A court order authorizing the use of pen registers and trap and trace may come from one of three sources:

  • An authorization under 18 U.S.C. 3123,  
  • An authorization under the Foreign Intelligence Surveillance Act of 1978; or
  • From a foreign government with an agreement with the U.S. Attorney General approved by the U.S. Attorney General.

When a government agency uses these devices under such authorization, they must use technology that only captures specific information like phone numbers or Internet addresses, not the actual content of the calls or messages. These restrictions strike a balance between the needs of law enforcement and individual privacy rights.

Illegal pen register or trap and trace device use is considered a misdemeanor under federal law. A conviction could result in up to one year in prison and a fine of up to $100,000.

What is the Exception to the Rule?

18 U.S.C. 3123 allows a specific exception for companies that provide phone or internet services. These companies may utilize pen registers or trap and trace devices without prior authorization for any of the following specific purposes:

  • For managing, maintaining, or testing their service,
  • To protect their rights or property,
  • To prevent the misuse or illegal use of their service,
  • To record when a call or online communication starts or ends to protect against fraud, illegal activities, misuse, or
  • If the person using the service agrees to it.

What Are Related Federal Laws?

18 U.S. Code Chapter 206, pen registers and trap and trace devices, has several federal laws related to section 3121, general prohibition on trace device use, such as the following: 

  • 18 U.S.C. 3122 - Application for an order for a pen register or a trap and trace device,
  • 18 U.S.C. 3123 - Issuance of an order for a pen register or a trap and trace device,
  • 18 U.S.C. 3124 - Assistance in the installation and use of a pen register or a trap and trace device,
  • 18 U.S.C. 3125 - Emergency pen register and trap and trace device installation,
  • 18 U.S.C. 3126 - Reports concerning pen registers and trap and trace devices,
  • 18 U.S.C. 3127 - Definitions for chapter.

How Can You Defend Against Charges Related to U.S.C. 3121?

If you're charged with unauthorized use of these tracking devices, a federal criminal defense attorney may utilize one or more defenses to counter the charges:

  • You were authorized. You can provide the court order showing authorization to implement the trace.
  • You qualify for the exception. You operate a communications company using tracing devices under the parameters listed above.
  • Lack of knowledge or intent. Prosecutors must prove intent to obtain a conviction. If you can show you were unaware that your actions violated federal law, that you had no intent to violate privacy, or that you were unaware that you had no authorization, the charges may be dismissed.

You can contact our law firm for more information. Eisner Gorin LLP has offices in Los Angeles, California.

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About the Author

Dmitry Gorin

Dmitry Gorin is a licensed attorney, who has been involved in criminal trial work and pretrial litigation since 1994. Before becoming partner in Eisner Gorin LLP, Mr. Gorin was a Senior Deputy District Attorney in Los Angeles Courts for more than ten years. As a criminal tri...

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