Do they make a size appropriate for conference rooms?

One afternoon in early September, an architect boarded his commuter train and became a cellphone vigilante. He sat down next to a 20-something woman who he said was “blabbing away” into her phone.

“She was using the word ‘like’ all the time. She sounded like a Valley Girl,” said the architect, Andrew, who declined to give his last name because what he did next was illegal.

Andrew reached into his shirt pocket and pushed a button on a black device the size of a cigarette pack. It sent out a powerful radio signal that cut off the chatterer’s cellphone transmission — and any others in a 30-foot radius.

“She kept talking into her phone for about 30 seconds before she realized there was no one listening on the other end,” he said. His reaction when he first discovered he could wield such power? “Oh, holy moly! Deliverance.”

As cellphone use has skyrocketed, making it hard to avoid hearing half a conversation in many public places, a small but growing band of rebels is turning to a blunt countermeasure: the cellphone jammer, a gadget that renders nearby mobile devices impotent.

Devices Enforce Silence of Cellphones, Illegally (New York Times, November 4, 2007)