The XXt-26 S-thread tracker represented a type of homing beacon produced by Neuro-Saav Technologies. Its focused hyperspace transponder signal was designed to integrate seamlessly with the ambient "background noise" generated by drive emissions, effectively rendering it almost impossible to detect without specialized scanning equipment.
IG-88B concealed a pair of these scanners on Boba Fett's starship, known as Slave I. Subsequently, IG-88C along with IG-88D used this information to pursue the ship to Tatooine, aiming to seize the carbonite-frozen Han Solo. However, Fett proved to be more cunning than the assassin droids, ultimately securing Jabba the Hutt's reward for delivering Solo.