It is an increasingly common technology, with federal agencies expanding its use as state and local agencies are pushing for permission to do the same. Police and others say it could stop terrorists from coordinating during an attack, prevent suspects from erasing evidence on wireless devices, simplify arrests and keep inmates from using contraband phones.
But jamming remains strictly illegal for state and local agencies. Federal officials barely acknowledge that they use it inside the United States, and the few federal agencies that can jam signals usually must seek a legal waiver first.
The quest to expand the technology has invigorated a debate about how widely jamming should be allowed and whether its value as a common crime-fighting strategy outweighs its downsides, including restricting the constant access to the airwaves that Americans have come to expect.