A roving wiretap is a warrant for a wiretap placed on a specific person rather than a "hardwire" tap on a specific phone. The term "wiretap" itself is obsolete and outdated, as the specific copper telephone lines have not themselves been "tapped" since the 1970s. So-called "wiretaps" have been done through switches and electronic radio intercepts for nearly 30s years. Nonetheless, the language used in legislation and court rulings has not kept pace with technological change, and leaving much room for confusion and poltical demagoguery.
Wiretaps authorized on persons rather than the communications hardware are very useful for law enforcement when a suspect has easy access to various cell phones, computers, pay phones, and private land lines. Before roving wiretaps, the FBI would need to get a separate FISC (Foreign Intelligence Surveillance Court) warrant for each method of communication used by a terrorist. With roving wiretaps, the FBI only needs to get one warrant, and tap whatever line the suspect happens to be using at the time.
The FISA Act which created the FISA Court itself has become outmoded, the original intent directed against foreign nation states, and did not adaquately consider the national security threat coming from no-state actors, such as terrorist organizations. Hence terrorists were able to exploit a loophole in the law.
- DeRosa, Mary. “Section 206: Roving Surveillance Authority Under FISA: A Summary” (American Bar Association, 2005).