Introduced by the Bush administration, the law passed through innumerable Congressional hearings that scrutinized every detail of law enforcement's requests. Mechanical switches require some work to wiretap, so they impose a practical restraint on how many wiretaps are installed. Unless specially designed to permit wiretapping, digital switches make it unworkable under some circumstances. Furthermore, new technology raises questions that never existed before. With traditional land-wire telephones, police never had to ask where a suspect was when making his call.
Mobile phones allow suspects to make calls from anywhere.
The legal system has offered constraints on wiretapping for a long time. Merely to learn the phone numbers that someone is calling, or being called from, requires a warrant and a court order. Retrieving the actual content of the call requires an order from a District Court. Furthermore, the police have to justify wiretapping as a last resort, by proving that the use of informers or other methods of collecting information is unfeasible or dangerous. They point out that computerized auditing techniques are also valuable, as they are at computer sites.