A signal jammer, also known as a communications jammer, was a device capable of jamming communications feeds.
During his time in the Senate of the Galactic Republic, Bail Organa sometimes made use of a signal jammer worn on his belt and concealed by the folds of his cape.
Gall Trayvis, a Senator of the Imperial Senate in exile, owned a signal jammer. He used his device to temporarily block Imperial feeds. They would shut him out quickly once they detected the intrusion, but before they could, he would take over the feed and make his own broadcasts, which Sabine Wren described in her personal journal as "a concentrated dose of the TRUTH," though Trayvis' messages were actually a cover intended to lure rebels into traps.