Annari ships emitting scanning pulses
A scanning pulse was an energy wave designed to detect starships traveling within a predetermined radius.
A Devore sensor array in the Delta Quadrant utilized scanning pulses with a range of ten light years, designed to detect warp fields and impulse signatures. Located near the Tehara system, the Devore used it as part of their organized campaign to locate and arrest telepaths traveling through their space. In 2375, the crew of the USS Voyager, who were attempting to transport a group of telepathic refugees to a wormhole in the Tehara system, eluded detection by one of the pulses by lowering the ship's power output to beneath the array's detection threshold. The pulse, however, triggered a variance in Voyager's antimatter stream, which would make the ship visible to the next pulse. Although Lieutenant B'Elanna Torres, Voyager's chief engineer, attempted to shut down the warp core to negate the problem, she experienced difficulties with the plasma injectors, and was unable to correct it in time to avoid detection by the next pulse. (VOY: "Counterpoint")
The Annari also used scanning pulses, designed to illuminate cloaked ships, as part of their blockade of the Kraylor homeworld. In 2377, Voyager officer Harry Kim, commanding a Kraylor vessel he had dubbed "Nightingale," successfully penetrated the pulses' perimeter, and fought off an Annari attack, allowing the Kraylor to retain their cloaking technology. (VOY: "Nightingale")