A trap and trace device is an electronic device used to record and trace all communication signals from a telecommunication system. An analogous feature available (usually at an additional charge) for use by the general public would be Caller ID.
Title 18 of the United States Code defines a trap and trace device as follows:
A trap and trace device is similar to a pen register. A trap and trace device would show what numbers had called a specific telephone, i.e. all incoming phone numbers. A pen register rather would show what numbers a phone had called, i.e. all outgoing phone numbers. The two terms are often used in concert, especially in the context of Internet communications. They are often jointly referred to as "Pen Register or Trap and Trace devices," to reflect the fact that the same program will probably do both functions in the modern era, and the distinction is not that important. The term 'pen register' is often used to describe both pen registers and trap and trace devices.
Trap and trace device is a Sunset Provision of the USA PATRIOT Act. Prior to the enacting of the USA PATRIOT Act, the Foreign Intelligence Surveillance Act was exempt from laws regarding the acquisition of "addressing information" such as: telephone conversations, personal letters, emails and all other electronic communications through the use of trap and trace devices. Along with giving the government easier access to communications between the sender and receiver, section 214 of PATRIOT ACT now has eliminated the prerequisite that the government prove that the suspect is, "an agent of foreign power". The use of trap and trace orders are still prohibited for activities that are protected under the First Amendment.