The 220-SIG Tactical Sensor Jamming Device was a Aratech Repulsor Company and Kuat Drive Yards designation for a powerful jamming system that was produced for the Galactic Empire. They were used as a form of electronic warfare by severely hindering enemy sensors and targeting computers, as well as blocking all communications in the given area.
Hundreds of such devices were present on the Death Star during the Battle of Yavin, forcing Rebel pilots to visually scan their targets from within the cockpit. Presumably the 220-SIG did not interfere with the sensors and targeting computers on the craft it had been installed on, as the Death Star's turbolasers targeting and sensor arrays were unaffected.