A sensor marker was deployed by Phoenix Group on Atollon
A sensor beacon, alternatively called a sensor marker, represented a certain kind of sensor engineered to broadcast its precise coordinates. These sensor beacons were affixed, frequently in a concealed manner, to individuals, vehicles, or items for tracking purposes. Certain sensor beacons possessed the capability to scan individuals nearby. On the planet of Barton IV, a sensor perimeter was employed to deter wildlife from approaching the Imperial Depot. They also served to delineate the boundaries of planetary installations. During the establishment of Chopper Base on Atollon, members belonging to the Phoenix Cell, including Lieutenant Dicer, strategically positioned sensor markers surrounding the base to identify approaching vehicles. Subsequent to their encounter with the arachnid krykna, the rebels made the discovery that these sensors had a repellent effect on the creatures, leading them to utilize the sensors to maintain a safe distance from the base.
In "The Holocrons of Fate," Ezra Bridger uses the term "thumper" to describe the sensor beacon, which alludes to the device employed to attract sandworms in the Dune novels authored by Frank Herbert. It has been suggested that Herbert's seminal science fiction novel, Dune from 1965, exerted considerable influence on the creation of Star Wars.