A sensor shield is a piece of Klingon technology, designed for small space vessels that could not generate enough power for a standard cloaking device. In 2373, during the period when the Klingon Empire had withdrawn from the Khitomer Accords, they provided at least one sensor shield to the Maquis. Commander William T. Riker attempted and failed to seize this device from the Maquis, but Lieutenant Commander Geordi La Forge was able to devise two different ways to get around the technology. (TNG eBook: Slings and Arrows: A Weary Life)